diff --git a/.rubocop.yml b/.rubocop.yml
index 48e25dba8..71ad1b1de 100644
--- a/.rubocop.yml
+++ b/.rubocop.yml
@@ -73,11 +73,17 @@ Metrics/MethodLength:
 RSpec/BeforeAfterAll:
   Enabled: false
 
+RSpec/ContextWording:
+  Enabled: false
+
 # Ideally, we'd use this one, too, but our tests have not historically followed
 # this style and it's not worth changing right now, IMO
 RSpec/DescribeClass:
   Enabled: false
 
+RSpec/ExampleLength:
+  Enabled: false
+
 Style/FetchEnvVar:
   Enabled: false
 
diff --git a/lib/bson/document.rb b/lib/bson/document.rb
index f46cab549..678a27479 100644
--- a/lib/bson/document.rb
+++ b/lib/bson/document.rb
@@ -36,6 +36,20 @@ module BSON
   # @since 2.0.0
   class Document < ::Hash
 
+    class << self
+      # Attempts to convert the provided object to a BSON::Document.
+      #
+      # @param [ Object ] object The object to try to convert.
+      #
+      # @return [ BSON::Document, nil ] The converted document or nil if it cannot be converted.
+      def try_convert(object)
+        return object if object.is_a?(BSON::Document)
+
+        hash = super
+        BSON::Document.new(hash) if hash
+      end
+    end
+
     # Get a value from the document for the provided key. Can use string or
     # symbol access, with string access being the faster of the two.
     #
@@ -60,7 +74,7 @@ class Document < ::Hash
     # @example Get an element for the key by symbol with a block default.
     #   document.fetch(:field) { |key| key.upcase }
     #
-    # @param [ String, Symbol ] key The key to look up.
+    # @param [ Object ] key The key to look up.
     # @param [ Object ] default Returned value if key does not exist.
     # @yield [key] Block returning default value for the given key.
     #
@@ -81,7 +95,7 @@ def fetch(key, *args, &block)
     # @example Get an element for the key by symbol.
     #   document[:field]
     #
-    # @param [ String, Symbol ] key The key to look up.
+    # @param [ Object ] key The key to look up.
     #
     # @return [ Object ] The found value, or nil if none found.
     #
@@ -106,8 +120,8 @@ def [](key)
     #
     # Note that due to this conversion, the object that is stored in the
     # receiver Document may be different from the object supplied as the
-    # right hand side of the assignment. In Ruby, the result of assignment
-    # is the right hand side, not the return value of []= method.
+    # right-hand side of the assignment. In Ruby, the result of assignment
+    # is the right-hand side, not the return value of []= method.
     # Because of this, modifying the result of assignment generally does not
     # work as intended:
     #
@@ -137,7 +151,7 @@ def [](key)
     # @example Set a value on the document.
     #   document[:test] = "value"
     #
-    # @param [ String, Symbol ] key The key to update.
+    # @param [ Object ] key The key to update.
     # @param [ Object ] value The value to update.
     #
     # @return [ Object ] The updated value.
@@ -147,7 +161,9 @@ def []=(key, value)
       super(convert_key(key), convert_value(value))
     end
 
-    # Returns true if the given key is present in the document.  Will normalize
+    alias :store :[]=
+
+    # Returns true if the given key is present in the document. Will normalize
     # symbol keys into strings.
     #
     # @example Test if a key exists using a symbol
@@ -155,7 +171,7 @@ def []=(key, value)
     #
     # @param [ Object ] key The key to check for.
     #
-    # @return [ true, false]
+    # @return [ true, false ] Whether the key exists in the document.
     #
     # @since 4.0.0
     def has_key?(key)
@@ -166,22 +182,60 @@ def has_key?(key)
     alias :key?     :has_key?
     alias :member?  :has_key?
 
-    # Returns true if the given value is present in the document.  Will normalize
+    # Returns true if the given value is present in the document. Will normalize
     # symbols into strings.
     #
     # @example Test if a key exists using a symbol
     #   document.has_value?(:test)
     #
-    # @param [ Object ] value THe value to check for.
+    # @param [ Object ] value The value to check for.
     #
-    # @return [ true, false]
+    # @return [ true, false ] Whether the value exists in the document.
     #
     # @since 4.0.0
     def has_value?(value)
       super(convert_value(value))
     end
 
-    alias :value :has_value?
+    alias :value? :has_value?
+
+    # Gets the values for the given keys.
+    #
+    # @param [ Array<Object> ] keys The keys to retrieve values for.
+    #
+    # @return [ Array<Object> ] The values for the given keys.
+    def values_at(*keys)
+      keys.map { |key| self[key] }
+    end
+
+    # Fetches the values for the given keys.
+    #
+    # @param [ Array<Object> ] keys The keys to fetch values for.
+    # @yield [ key ] A block to execute when a key is not found.
+    #
+    # @return [ Array<Object> ] The values for the given keys.
+    #
+    # @raise [ KeyError ] If a key is not found and no block is given.
+    def fetch_values(*keys, &block)
+      keys.map do |key|
+        if block_given? && !key?(key)
+          yield(convert_key(key))
+        else
+          fetch(key)
+        end
+      end
+    end
+
+    # Searches for a key-value pair with the given key and returns
+    # the first matching pair found as a two-element array.
+    #
+    # @param [ Object ] key The key to search for.
+    #
+    # @return [ Array, nil ] A [key, value] pair, or nil if not found.
+    def assoc(key)
+      pair = super(convert_key(key))
+      pair ? [pair[0], pair[1]] : nil
+    end
 
     # Deletes the key-value pair and returns the value from the document
     # whose key is equal to key.
@@ -189,12 +243,10 @@ def has_value?(value)
     # block is given and the key is not found, pass in the key and return the
     # result of block.
     #
-    # @example Delete a key-value pair
-    #   document.delete(:test)
-    #
     # @param [ Object ] key The key of the key-value pair to delete.
+    # @yield [ key ] Optional block to execute when key is not found.
     #
-    # @return [ Object ]
+    # @return [ Object ] The value that was deleted or the default result.
     #
     # @since 4.0.0
     def delete(key, &block)
@@ -218,10 +270,8 @@ def initialize(elements = nil)
     # Merge this document with another document, returning a new document in
     # the process.
     #
-    # @example Merge with another document.
-    #   document.merge(name: "Bob")
-    #
     # @param [ BSON::Document, Hash ] other The document/hash to merge with.
+    # @yield [ key, old_value, new_value ] Optional block for resolving conflicts.
     #
     # @return [ BSON::Document ] The result of the merge.
     #
@@ -233,10 +283,8 @@ def merge(other, &block)
     # Merge this document with another document, returning the same document in
     # the process.
     #
-    # @example Merge with another document.
-    #   document.merge(name: "Bob")
-    #
     # @param [ BSON::Document, Hash ] other The document/hash to merge with.
+    # @yield [ key, old_value, new_value ] Optional block for resolving conflicts.
     #
     # @return [ BSON::Document ] The result of the merge.
     #
@@ -251,37 +299,28 @@ def merge!(other)
 
     alias :update :merge!
 
-    if instance_methods.include?(:dig)
-      # Retrieves the value object corresponding to the each key objects repeatedly.
-      # Will normalize symbol keys into strings.
-      #
-      # @example Get value from nested sub-documents, handling missing levels.
-      #   document # => { :key1 => { "key2" => "value"}}
-      #   document.dig(:key1, :key2) # => "value"
-      #   document.dig("key1", "key2") # => "value"
-      #   document.dig("foo", "key2") # => nil
-      #
-      # @param [ Array<String, Symbol> ] *keys Keys, which constitute a "path" to the nested value.
-      #
-      # @return [ Object, NilClass ] The requested value or nil.
-      #
-      # @since 3.0.0
-      def dig(*keys)
-        super(*keys.map{|key| convert_key(key)})
-      end
+    # Retrieves the value object corresponding to the each key objects repeatedly.
+    # Will normalize symbol keys into strings.
+    #
+    # @example Get value from nested sub-documents, handling missing levels.
+    #   document # => { :key1 => { "key2" => "value"}}
+    #   document.dig(:key1, :key2) # => "value"
+    #   document.dig("key1", "key2") # => "value"
+    #   document.dig("foo", "key2") # => nil
+    #
+    # @param [ Array<Object> ] keys Keys which constitute a path to the nested value.
+    #
+    # @return [ Object, NilClass ] The requested value or nil.
+    #
+    # @since 3.0.0
+    def dig(*keys)
+      super(*keys.map { |key| convert_key(key) })
     end
 
     # Slices a document to include only the given keys.
     # Will normalize symbol keys into strings.
-    # (this method is backported from ActiveSupport::Hash)
-    #
-    # @example Get a document/hash with only the `name` and `age` fields present
-    #   document # => { _id: <ObjectId>, :name => "John", :age => 30, :location => "Earth" }
-    #   document.slice(:name, 'age') # => { "name": "John", "age" => 30 }
-    #   document.slice('name') # => { "name" => "John" }
-    #   document.slice(:foo) # => {}
     #
-    # @param [ Array<String, Symbol> ] *keys Keys, that will be kept in the resulting document
+    # @param [ Array<Object> ] keys Keys that will be kept in the resulting document
     #
     # @return [ BSON::Document ] The document with only the selected keys
     #
@@ -299,11 +338,7 @@ def slice(*keys)
     #
     # The keys to be removed can be specified as either strings or symbols.
     #
-    # @example Get a document/hash with only the `name` and `age` fields removed
-    #   document # => { _id: <ObjectId>, :name => 'John', :age => 30, :location => 'Earth' }
-    #   document.except(:name, 'age') # => { _id: <ObjectId>, location: 'Earth' }
-    #
-    # @param [ Array<String, Symbol> ] *keys Keys, that will be removed in the resulting document
+    # @param [ Array<Object> ] keys Keys that will be removed in the resulting document.
     #
     # @return [ BSON::Document ] The document with the specified keys removed.
     #
@@ -312,13 +347,148 @@ def slice(*keys)
     #   its version of #except which doesn't work for BSON::Document which
     #   causes problems if ActiveSupport is loaded after bson-ruby is.
     def except(*keys)
-      copy = dup
-      keys.each {|key| copy.delete(key)}
-      copy
+      dup.tap do |doc|
+        keys.each { |key| doc.delete(key) }
+      end
+    end
+
+    alias :without :except
+
+    # Recursively converts the document and all nested documents to a hash.
+    #
+    # @note #to_h only converts the top-level document to a hash. #to_hash
+    #   converts all nested documents to hashes as well. This follows the
+    #   convention of ActiveSupport::HashWithIndifferentAccess
+    #
+    # @return [ Hash ] A new hash object, containing nested hashes if applicable.
+    #
+    # @note Code lovingly borrowed from ActiveSupport::HashWithIndifferentAccess.
+    def to_hash
+      ::Hash.new.tap do |hash|
+        set_defaults(hash)
+        each do |key, value|
+          hash[key] = value.is_a?(self.class) ? value.to_hash : value
+        end
+      end
+    end
+
+    # Returns a new document with all nil-valued key pairs removed.
+    #
+    # @return [ BSON::Document ] A new compacted document.
+    def compact
+      dup.tap { |doc| doc.compact! }
     end
 
+    # Inverts the document by using values as keys and vice versa.
+    #
+    # @return [ BSON::Document ] A new document with keys and values switched.
+    def invert
+      self.class.new(super)
+    end
+
+    # Returns a new document containing key-value pairs for which the block returns true.
+    #
+    # @yield [ key, value ] Each key-value pair in the document.
+    #
+    # @return [ BSON::Document ] A new document with matching pairs, or an Enumerator if no block given.
+    def select(&block)
+      return enum_for(:select) unless block_given?
+
+      dup.tap { |doc| doc.select!(&block) }
+    end
+
+    alias :filter :select
+
+    # Returns a new document excluding pairs for which the block returns true.
+    #
+    # @yield [ key, value ] Each key-value pair in the document.
+    #
+    # @return [ BSON::Document ] A new document without matching pairs, or an Enumerator if no block given.
+    def reject(&block)
+      return enum_for(:reject) unless block_given?
+
+      dup.tap { |doc| doc.reject!(&block) }
+    end
+
+    # Transforms all keys in the document using the given block.
+    #
+    # @yield [ key ] Each key in the document.
+    #
+    # @return [ BSON::Document ] A new document with transformed keys, or an Enumerator if no block given.
+    def transform_keys(&block)
+      return enum_for(:transform_keys) unless block_given?
+
+      dup.transform_keys!(&block)
+    end
+
+    # Transforms all keys in the document in place using the given block.
+    #
+    # @yield [ key ] Each key in the document.
+    #
+    # @return [ BSON::Document ] The document with transformed keys, or an Enumerator if no block given.
+    def transform_keys!
+      return enum_for(:transform_keys!) unless block_given?
+
+      super { |key| convert_key(yield(key)) }
+    end
+
+    # Transforms all values in the document using the given block.
+    #
+    # @yield [ value ] Each value in the document.
+    #
+    # @return [ BSON::Document ] A new document with transformed values, or an Enumerator if no block given.
+    def transform_values(&block)
+      return enum_for(:transform_values) unless block_given?
+
+      dup.transform_values!(&block)
+    end
+
+    # Transforms all values in the document in place using the given block.
+    #
+    # @yield [ value ] Each value in the document.
+    #
+    # @return [ BSON::Document ] The document with transformed values, or an Enumerator if no block given.
+    def transform_values!
+      return enum_for(:transform_values!) unless block_given?
+
+      super { |value| convert_value(yield(value)) }
+    end
+
+    # Returns a new hash with all keys converted to strings.
+    #
+    # @return [ BSON::Document ] A new document with string keys.
+    def stringify_keys
+      dup.stringify_keys!
+    end
+
+    # Returns a new hash with all keys converted to symbols.
+    #
+    # @return [ Hash ] A new hash with symbol keys.
+    def symbolize_keys
+      to_h.symbolize_keys!
+    end
+
+    # Raises an error because BSON::Document enforces string keys internally,
+    # and hence cannot be destructively modified to use symbol keys.
+    #
+    # @raise [ ArgumentError ] Indicates the method is not supported.
     def symbolize_keys!
-      raise ArgumentError, 'symbolize_keys! is not supported on BSON::Document instances. Please convert the document to hash first (using #to_h), then call #symbolize_keys! on the Hash instance'
+      raise ArgumentError, 'symbolize_keys! is not supported on BSON::Document instances. Instead call #symbolize_keys which returns a new Hash object.'
+    end
+
+    # Returns a new hash with all keys (top-level and nested) as symbols.
+    #
+    # @return [ Hash ] A new hash with all keys as symbols.
+    def deep_symbolize_keys
+      to_hash.deep_symbolize_keys!
+    end
+
+    # Raises an error because BSON::Document enforces string keys internally,
+    # and hence cannot be destructively modified to use symbol keys.
+    #
+    # @raise [ ArgumentError ] Indicates the method is not supported.
+    def deep_symbolize_keys!
+      raise ArgumentError, 'deep_symbolize_keys! is not supported on BSON::Document instances. Instead call #deep_symbolize_keys which returns a new Hash object.'
     end
 
     # Override the Hash implementation of to_bson_normalized_value.
@@ -326,8 +496,8 @@ def symbolize_keys!
     # BSON::Document is already of the correct type and already provides
     # indifferent access to keys, hence no further conversions are necessary.
     #
-    # Attempting to perform Hash's conversion on Document instances converts
-    # DBRefs to Documents which is wrong.
+    # Attempting to perform Hash's conversion on BSON::Document instances converts
+    # DBRef to BSON::Document which is wrong.
     #
     # @return [ BSON::Document ] The normalized hash.
     def to_bson_normalized_value
@@ -343,5 +513,14 @@ def convert_key(key)
     def convert_value(value)
       value.to_bson_normalized_value
     end
+
+    # @note Code lovingly borrowed from ActiveSupport::HashWithIndifferentAccess.
+    def set_defaults(target)
+      if default_proc
+        target.default_proc = default_proc.dup
+      else
+        target.default = default
+      end
+    end
   end
 end
diff --git a/spec/bson/document_as_spec.rb b/spec/bson/document_as_spec.rb
index 984c116c9..7d1f59bee 100644
--- a/spec/bson/document_as_spec.rb
+++ b/spec/bson/document_as_spec.rb
@@ -1,4 +1,5 @@
-# rubocop:todo all
+# frozen_string_literal: true
+
 # Copyright (C) 2021 MongoDB Inc.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -13,34 +14,999 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-require "spec_helper"
+require 'spec_helper'
 
-# BSON::Document ActiveSupport extensions
+# BSON::Document tests for ActiveSupport Hash extension method behaviors
 describe BSON::Document do
   require_active_support
 
+  let(:document) do
+    described_class.new('key1' => 'value1', 'key2' => 'value2', 'key3' => 'value3')
+  end
+
   describe '#symbolize_keys' do
-    context 'string keys' do
-      let(:doc) do
-        described_class.new('foo' => 'bar')
+    let(:result) do
+      document.symbolize_keys
+    end
+
+    it 'returns a Hash, not a BSON::Document' do
+      expect(result).to be_a(Hash)
+      expect(result).not_to be_a(described_class)
+    end
+
+    it 'converts string keys to symbols' do
+      expect(result).to eq({ key1: 'value1', key2: 'value2', key3: 'value3' })
+    end
+
+    it 'does not modify the original document' do
+      result
+      expect(document).to eq(described_class.new('key1' => 'value1', 'key2' => 'value2', 'key3' => 'value3'))
+    end
+
+    context 'with nested documents' do
+      let(:document) do
+        described_class.new('key1' => described_class.new('inner' => 'value'))
       end
 
-      it 'works correctly' do
-        doc.symbolize_keys.should == {foo: 'bar'}
+      let(:result) do
+        document.symbolize_keys
+      end
+
+      it 'does not convert keys in nested documents' do
+        expect(result[:key1]).to eq({ 'inner' => 'value' })
+      end
+
+      it 'does not convert nested BSON::Document to plain Hashes' do
+        expect(result[:key1]).to be_a(described_class)
       end
     end
   end
 
   describe '#symbolize_keys!' do
-    context 'string keys' do
-      let(:doc) do
-        described_class.new('foo' => 'bar')
+    it 'raises ArgumentError' do
+      expect { document.symbolize_keys! }.to raise_error(ArgumentError, /symbolize_keys! is not supported/)
+    end
+  end
+
+  describe '#deep_symbolize_keys' do
+    let(:document) do
+      described_class.new('key1' => 'value1', 'key2' => described_class.new('inner' => 'value'))
+    end
+
+    let(:result) do
+      document.deep_symbolize_keys
+    end
+
+    it 'returns a Hash, not a BSON::Document' do
+      expect(result).to be_a(Hash)
+      expect(result).not_to be_a(described_class)
+    end
+
+    it 'converts string keys to symbols at all levels' do
+      expect(result).to eq({ key1: 'value1', key2: { inner: 'value' } })
+    end
+
+    it 'does not modify the original document' do
+      result
+      expect(document).to eq(described_class.new('key1' => 'value1', 'key2' => described_class.new('inner' => 'value')))
+    end
+  end
+
+  describe '#deep_symbolize_keys!' do
+    let(:document) do
+      described_class.new('key1' => 'value1', 'key2' => described_class.new('inner' => 'value'))
+    end
+
+    it 'raises ArgumentError' do
+      expect { document.deep_symbolize_keys! }.to raise_error(ArgumentError, /deep_symbolize_keys! is not supported/)
+    end
+  end
+
+  describe '#stringify_keys' do
+    let(:document) do
+      described_class.new(1 => 'value1', 'key2' => { 3 => :value3 })
+    end
+
+    let(:result) do
+      document.stringify_keys
+    end
+
+    it 'returns a new BSON::Document' do
+      expect(result).to be_a(described_class)
+      expect(result).not_to be(document)
+    end
+
+    it 'modifies only the top-level document keys' do
+      expect(result).to eq('1' => 'value1', 'key2' => { 3 => :value3 })
+    end
+  end
+
+  describe '#stringify_keys!' do
+    let(:document) do
+      described_class.new(1 => 'value1', 'key2' => { 3 => :value3 })
+    end
+
+    let(:result) do
+      document.stringify_keys!
+    end
+
+    it 'returns self' do
+      expect(result).to be(document)
+    end
+
+    it 'modifies only the top-level document keys' do
+      result
+      expect(document).to eq('1' => 'value1', 'key2' => { 3 => :value3 })
+    end
+  end
+
+  describe '#deep_stringify_keys' do
+    let(:document) do
+      described_class.new(1 => 'value1', 'key2' => { 3 => :value3 })
+    end
+
+    let(:result) do
+      document.deep_stringify_keys
+    end
+
+    it 'returns a Hash' do
+      expect(result).to be_a(Hash)
+    end
+
+    it 'converts all keys to strings at all levels' do
+      expect(result).to eq({ '1' => 'value1', 'key2' => { '3' => :value3 } })
+    end
+
+    it 'converts nested documents to Hash' do
+      expect(result['key2']).to be_a(Hash)
+    end
+  end
+
+  describe '#deep_stringify_keys!' do
+    let(:document) do
+      described_class.new(1 => 'value1', 'key2' => { 3 => :value3 })
+    end
+
+    let(:result) do
+      document.deep_stringify_keys!
+    end
+
+    it 'returns self' do
+      expect(result).to be(document)
+    end
+
+    it 'modifies only the all levels of document keys' do
+      result
+      expect(document).to eq('1' => 'value1', 'key2' => { '3' => :value3 })
+    end
+  end
+
+  describe '#slice!' do
+    let(:result) do
+      document.slice!('key1', 'key3')
+    end
+
+    it 'returns a new BSON::Document with removed keys' do
+      expect(result).to be_a(described_class)
+      expect(result).to eq(described_class.new('key2' => 'value2'))
+    end
+
+    it 'modifies the original document' do
+      result
+      expect(document).to eq(described_class.new('key1' => 'value1', 'key3' => 'value3'))
+    end
+
+    context 'when some keys do not exist' do
+      let(:document) do
+        described_class.new('key1' => 'value1', 'key2' => 'value2')
+      end
+
+      let(:result) do
+        document.slice!('key1', 'nonexistent')
+      end
+
+      it 'returns a document with the keys that were removed' do
+        expect(result).to eq(described_class.new('key2' => 'value2'))
+      end
+
+      it 'modifies the original document' do
+        result
+        expect(document).to eq(described_class.new('key1' => 'value1'))
+      end
+    end
+
+    context 'with symbol keys' do
+      let(:document) do
+        described_class.new(key1: 'value1', key2: 'value2')
+      end
+
+      let(:result) do
+        document.slice!('key1')
+      end
+
+      it 'returns a document with the keys that were removed' do
+        expect(result).to eq(described_class.new('key2' => 'value2'))
+      end
+
+      it 'modifies the original document' do
+        result
+        expect(document).to eq(described_class.new('key1' => 'value1'))
+      end
+    end
+  end
+
+  describe '#deep_merge' do
+    let(:document) do
+      described_class.new('key1' => 'value1', 'key2' => 'value2')
+    end
+
+    context 'when merging with a simple hash' do
+      let(:other) do
+        { 'key2' => 'new_value', 'key3' => 'value3' }
+      end
+
+      let(:result) do
+        document.deep_merge(other)
+      end
+
+      it 'returns a new BSON::Document' do
+        expect(result).to be_a(described_class)
+        expect(result).not_to be(document)
+      end
+
+      it 'includes all keys from both documents' do
+        expect(result.keys).to include('key1', 'key2', 'key3')
+      end
+
+      it 'overwrites values for duplicate keys' do
+        expect(result['key2']).to eq('new_value')
+      end
+
+      it 'does not modify the original document' do
+        expect(document['key2']).to eq('value2')
+        expect(document.keys).not_to include('key3')
+      end
+    end
+
+    context 'when merging with a nested hash' do
+      let(:document) do
+        described_class.new(
+          'key1' => 'value1',
+          'nested' => described_class.new(
+            'inner1' => 'value1',
+            'inner2' => 'value2'
+          )
+        )
+      end
+
+      let(:other) do
+        {
+          'key2' => 'value2',
+          'nested' => {
+            'inner2' => 'new_value',
+            'inner3' => 'value3'
+          }
+        }
+      end
+
+      let(:result) do
+        document.deep_merge(other)
+      end
+
+      it 'returns a new BSON::Document' do
+        expect(result).to be_a(described_class)
+        expect(result).not_to be(document)
+      end
+
+      it 'includes top-level keys from both documents' do
+        expect(result.keys).to include('key1', 'key2', 'nested')
+      end
+
+      it 'deeply merges nested documents' do
+        expect(result['nested'].keys).to include('inner1', 'inner2', 'inner3')
+        expect(result['nested']['inner1']).to eq('value1')
+        expect(result['nested']['inner2']).to eq('new_value')
+        expect(result['nested']['inner3']).to eq('value3')
+      end
+
+      it 'returns nested documents as BSON::Document' do
+        expect(result['nested']).to be_a(described_class)
+      end
+
+      it 'does not modify the original document' do
+        expect(document['nested']['inner2']).to eq('value2')
+        expect(document['nested'].keys).not_to include('inner3')
+      end
+    end
+
+    context 'when merging with deeply nested hashes' do
+      let(:document) do
+        described_class.new(
+          'level1' => described_class.new(
+            'level2' => described_class.new(
+              'level3' => described_class.new(
+                'a' => 1,
+                'b' => 2
+              )
+            )
+          )
+        )
+      end
+
+      let(:other) do
+        {
+          'level1' => {
+            'level2' => {
+              'level3' => {
+                'b' => 3,
+                'c' => 4
+              },
+              'new_key' => 'value'
+            }
+          }
+        }
+      end
+
+      let(:result) do
+        document.deep_merge(other)
+      end
+
+      it 'merges documents at all levels' do
+        expect(result['level1']['level2']['level3']['a']).to eq(1)
+        expect(result['level1']['level2']['level3']['b']).to eq(3)
+        expect(result['level1']['level2']['level3']['c']).to eq(4)
+        expect(result['level1']['level2']['new_key']).to eq('value')
+      end
+
+      it 'returns BSON::Document at all nested levels' do
+        expect(result['level1']).to be_a(described_class)
+        expect(result['level1']['level2']).to be_a(described_class)
+        expect(result['level1']['level2']['level3']).to be_a(described_class)
+      end
+    end
+
+    context 'when merging with arrays' do
+      let(:document) do
+        described_class.new(
+          'key1' => 'value1',
+          'array' => [ 1, 2, 3 ],
+          'nested' => described_class.new(
+            'array' => [ 4, 5, 6 ]
+          )
+        )
+      end
+
+      let(:other) do
+        {
+          'key2' => 'value2',
+          'array' => [ 7, 8, 9 ],
+          'nested' => {
+            'array' => [ 10, 11, 12 ]
+          }
+        }
+      end
+
+      let(:result) do
+        document.deep_merge(other)
+      end
+
+      it 'replaces arrays instead of merging them' do
+        expect(result['array']).to eq([ 7, 8, 9 ])
+        expect(result['nested']['array']).to eq([ 10, 11, 12 ])
+      end
+    end
+
+    context 'when merging with non-hash values' do
+      let(:document) do
+        described_class.new(
+          'key1' => 'value1',
+          'key2' => described_class.new('inner' => 'value')
+        )
+      end
+
+      let(:other) do
+        {
+          'key1' => 'new_value',
+          'key2' => 'not_a_hash'
+        }
+      end
+
+      let(:result) do
+        document.deep_merge(other)
+      end
+
+      it 'overwrites non-hash values' do
+        expect(result['key1']).to eq('new_value')
+        expect(result['key2']).to eq('not_a_hash')
+      end
+    end
+
+    context 'when a block is provided' do
+      let(:document) do
+        described_class.new(
+          'key1' => 'value1',
+          'nested' => described_class.new(
+            'inner' => 5
+          )
+        )
+      end
+
+      let(:other) do
+        {
+          'key1' => 'new_value',
+          'nested' => {
+            'inner' => 10
+          }
+        }
+      end
+
+      let(:result) do
+        document.deep_merge(other) do |key, old_value, new_value|
+          if key == 'inner' && old_value.is_a?(Integer) && new_value.is_a?(Integer)
+            old_value + new_value
+          else
+            new_value
+          end
+        end
+      end
+
+      it 'applies the block to resolve conflicts' do
+        expect(result['key1']).to eq('new_value')
+        expect(result['nested']['inner']).to eq(15) # 5 + 10
+      end
+    end
+  end
+
+  describe '#deep_merge!' do
+    let(:document) do
+      described_class.new('key1' => 'value1', 'key2' => 'value2')
+    end
+
+    context 'when merging with a simple hash' do
+      let(:other) do
+        { 'key2' => 'new_value', 'key3' => 'value3' }
+      end
+
+      let(:result) do
+        document.deep_merge!(other)
+      end
+
+      it 'returns self' do
+        expect(result).to be(document)
+      end
+
+      it 'includes all keys from both documents' do
+        result
+        expect(document.keys).to include('key1', 'key2', 'key3')
+      end
+
+      it 'overwrites values for duplicate keys' do
+        result
+        expect(document['key2']).to eq('new_value')
+      end
+    end
+
+    context 'when merging with a nested hash' do
+      let(:document) do
+        described_class.new(
+          'key1' => 'value1',
+          'nested' => described_class.new(
+            'inner1' => 'value1',
+            'inner2' => 'value2'
+          )
+        )
+      end
+
+      let(:other) do
+        {
+          'key2' => 'value2',
+          'nested' => {
+            'inner2' => 'new_value',
+            'inner3' => 'value3'
+          }
+        }
+      end
+
+      let(:result) do
+        document.deep_merge!(other)
+      end
+
+      it 'returns self' do
+        expect(result).to be(document)
+      end
+
+      it 'includes top-level keys from both documents' do
+        result
+        expect(document.keys).to include('key1', 'key2', 'nested')
+      end
+
+      it 'deeply merges nested documents' do
+        result
+        expect(document['nested'].keys).to include('inner1', 'inner2', 'inner3')
+        expect(document['nested']['inner1']).to eq('value1')
+        expect(document['nested']['inner2']).to eq('new_value')
+        expect(document['nested']['inner3']).to eq('value3')
+      end
+
+      it 'returns nested documents as BSON::Document' do
+        result
+        expect(document['nested']).to be_a(described_class)
+      end
+    end
+
+    context 'when merging with deeply nested hashes' do
+      let(:document) do
+        described_class.new(
+          'level1' => described_class.new(
+            'level2' => described_class.new(
+              'level3' => described_class.new(
+                'a' => 1,
+                'b' => 2
+              )
+            )
+          )
+        )
+      end
+
+      let(:other) do
+        {
+          'level1' => {
+            'level2' => {
+              'level3' => {
+                'b' => 3,
+                'c' => 4
+              },
+              'new_key' => 'value'
+            }
+          }
+        }
+      end
+
+      let(:result) do
+        document.deep_merge!(other)
+      end
+
+      it 'merges documents at all levels' do
+        result
+        expect(document['level1']['level2']['level3']['a']).to eq(1)
+        expect(document['level1']['level2']['level3']['b']).to eq(3)
+        expect(document['level1']['level2']['level3']['c']).to eq(4)
+        expect(document['level1']['level2']['new_key']).to eq('value')
+      end
+
+      it 'returns BSON::Document at all nested levels' do
+        result
+        expect(document['level1']).to be_a(described_class)
+        expect(document['level1']['level2']).to be_a(described_class)
+        expect(document['level1']['level2']['level3']).to be_a(described_class)
+      end
+    end
+
+    context 'when merging with arrays' do
+      let(:document) do
+        described_class.new(
+          'key1' => 'value1',
+          'array' => [ 1, 2, 3 ],
+          'nested' => described_class.new(
+            'array' => [ 4, 5, 6 ]
+          )
+        )
+      end
+
+      let(:other) do
+        {
+          'key2' => 'value2',
+          'array' => [ 7, 8, 9 ],
+          'nested' => {
+            'array' => [ 10, 11, 12 ]
+          }
+        }
+      end
+
+      let(:result) do
+        document.deep_merge!(other)
+      end
+
+      it 'replaces arrays instead of merging them' do
+        result
+        expect(document['array']).to eq([ 7, 8, 9 ])
+        expect(document['nested']['array']).to eq([ 10, 11, 12 ])
+      end
+    end
+
+    context 'when merging with non-hash values' do
+      let(:document) do
+        described_class.new(
+          'key1' => 'value1',
+          'key2' => described_class.new('inner' => 'value')
+        )
+      end
+
+      let(:other) do
+        {
+          'key1' => 'new_value',
+          'key2' => 'not_a_hash'
+        }
+      end
+
+      let(:result) do
+        document.deep_merge!(other)
+      end
+
+      it 'overwrites non-hash values' do
+        result
+        expect(document['key1']).to eq('new_value')
+        expect(document['key2']).to eq('not_a_hash')
+      end
+    end
+
+    context 'when a block is provided' do
+      let(:document) do
+        described_class.new(
+          'key1' => 'value1',
+          'nested' => described_class.new(
+            'inner' => 5
+          )
+        )
+      end
+
+      let(:other) do
+        {
+          'key1' => 'new_value',
+          'nested' => {
+            'inner' => 10
+          }
+        }
+      end
+
+      let(:result) do
+        document.deep_merge!(other) do |key, old_value, new_value|
+          if key == 'inner' && old_value.is_a?(Integer) && new_value.is_a?(Integer)
+            old_value + new_value
+          else
+            new_value
+          end
+        end
+      end
+
+      it 'applies the block to resolve conflicts' do
+        result
+        expect(document['key1']).to eq('new_value')
+        expect(document['nested']['inner']).to eq(15) # 5 + 10
+      end
+    end
+
+    context 'when merging with nil values' do
+      let(:document) do
+        described_class.new(
+          'key1' => 'value1',
+          'key2' => 'value2'
+        )
+      end
+
+      let(:other) do
+        {
+          'key1' => nil,
+          'key3' => nil
+        }
+      end
+
+      let(:result) do
+        document.deep_merge!(other)
+      end
+
+      it 'overwrites existing values with nil' do
+        result
+        expect(document['key1']).to be_nil
+      end
+
+      it 'adds new keys with nil values' do
+        result
+        expect(document.key?('key3')).to be true
+        expect(document['key3']).to be_nil
+      end
+    end
+
+    context 'when merging with deeply nested identical structures' do
+      let(:document) do
+        described_class.new(
+          'config' => described_class.new(
+            'options' => described_class.new(
+              'timeout' => 30,
+              'retry' => true
+            )
+          )
+        )
+      end
+
+      let(:other) do
+        {
+          'config' => {
+            'options' => {
+              'timeout' => 60
+            }
+          }
+        }
+      end
+
+      let(:result) do
+        document.deep_merge!(other)
+      end
+
+      it 'preserves unmodified nested values' do
+        result
+        expect(document['config']['options']['retry']).to be true
+      end
+
+      it 'updates modified nested values' do
+        result
+        expect(document['config']['options']['timeout']).to eq(60)
+      end
+
+      it 'maintains the BSON::Document class throughout the structure' do
+        result
+        expect(document['config']).to be_a(described_class)
+        expect(document['config']['options']).to be_a(described_class)
+      end
+    end
+
+    context 'when the type of a nested structure changes' do
+      let(:document) do
+        described_class.new(
+          'key' => described_class.new(
+            'was_hash' => true
+          )
+        )
+      end
+
+      let(:other) do
+        {
+          'key' => 'now a string'
+        }
+      end
+
+      let(:result) do
+        document.deep_merge!(other)
+      end
+
+      it 'replaces the nested structure with the new type' do
+        result
+        expect(document['key']).to eq('now a string')
+      end
+    end
+  end
+
+  describe '#extract!' do
+    context 'with string keys' do
+      let(:extracted) do
+        document.extract!('key1', 'key3')
+      end
+
+      it 'returns a document with extracted pairs' do
+        expect(extracted).to be_a(described_class)
+        expect(extracted).to eq(described_class.new('key1' => 'value1', 'key3' => 'value3'))
+      end
+
+      it 'removes extracted pairs from original document' do
+        extracted
+        expect(document).to eq(described_class.new('key2' => 'value2'))
+      end
+    end
+
+    context 'with symbol keys' do
+      let(:extracted) do
+        document.extract!(:key1, :key3)
+      end
+
+      it 'returns a document with extracted pairs' do
+        expect(extracted).to be_a(described_class)
+        expect(extracted).to eq(described_class.new('key1' => 'value1', 'key3' => 'value3'))
+      end
+    end
+
+    context 'with missing keys' do
+      let(:extracted) do
+        document.extract!('key1', 'missing')
+      end
+
+      it 'ignores missing keys' do
+        expect(extracted).to eq(described_class.new('key1' => 'value1'))
+      end
+    end
+
+    context 'with nested documents' do
+      let(:document) do
+        described_class.new(
+          'key1' => 'value1',
+          'nested' => described_class.new('inner1' => 'nested_value1', 'inner2' => 'nested_value2')
+        )
+      end
+
+      let(:extracted) do
+        document.extract!('key1', 'nested')
+      end
+
+      it 'returns nested documents as BSON::Documents' do
+        expect(extracted['nested']).to be_a(described_class)
+      end
+    end
+  end
+
+  describe '#without' do
+    context 'with string keys' do
+      let(:result) do
+        document.without('key1', 'key3')
+      end
+
+      it 'returns a document without the specified keys' do
+        expect(result).to be_a(described_class)
+        expect(result).to eq(described_class.new('key2' => 'value2'))
+      end
+
+      it 'does not modify the original document' do
+        result
+        expect(document).to eq(
+          described_class.new('key1' => 'value1', 'key2' => 'value2', 'key3' => 'value3')
+        )
+      end
+    end
+
+    context 'with symbol keys' do
+      let(:result) do
+        document.without(:key1, :key3)
+      end
+
+      it 'returns a document without the specified keys' do
+        expect(result).to eq(described_class.new('key2' => 'value2'))
+      end
+    end
+
+    context 'with missing keys' do
+      let(:result) do
+        document.without('key1', 'missing')
+      end
+
+      it 'ignores missing keys' do
+        expect(result).to eq(described_class.new('key2' => 'value2', 'key3' => 'value3'))
+      end
+    end
+  end
+
+  describe '#with_indifferent_access' do
+    let(:document) do
+      described_class.new('key1' => 'value1', :key2 => 'value2')
+    end
+
+    let(:result) do
+      document.with_indifferent_access
+    end
+
+    it 'returns a HashWithIndifferentAccess' do
+      expect(result).to be_a(ActiveSupport::HashWithIndifferentAccess)
+    end
+
+    it 'allows access with both strings and symbols' do
+      expect(result['key1']).to eq('value1')
+      expect(result[:key1]).to eq('value1')
+      expect(result['key2']).to eq('value2')
+      expect(result[:key2]).to eq('value2')
+    end
+
+    context 'with nested documents' do
+      let(:document) do
+        described_class.new(
+          'key1' => 'value1',
+          'nested' => described_class.new('inner' => 'value')
+        )
+      end
+
+      let(:result) do
+        document.with_indifferent_access
+      end
+
+      it 'converts nested documents to HashWithIndifferentAccess' do
+        expect(result[:nested]).to be_a(ActiveSupport::HashWithIndifferentAccess)
+        expect(result[:nested][:inner]).to eq('value')
+        expect(result['nested']['inner']).to eq('value')
+      end
+    end
+  end
+
+  describe '#compact_blank' do
+    let(:document) do
+      described_class.new(
+        'key1' => 'value1',
+        'key2' => '',
+        'key3' => nil,
+        'key4' => [],
+        'key5' => {}
+      )
+    end
+
+    let(:result) do
+      document.compact_blank
+    end
+
+    it 'returns a BSON::Document' do
+      expect(result).to be_a(described_class)
+    end
+
+    it 'removes blank values' do
+      expect(result.keys).to eq([ 'key1' ])
+      expect(result['key1']).to eq('value1')
+    end
+
+    it 'does not modify the original document' do
+      result
+      expect(document.keys).to eq(%w[key1 key2 key3 key4 key5])
+    end
+
+    context 'with nested documents' do
+      let(:document) do
+        described_class.new(
+          'key1' => 'value1',
+          'nested' => described_class.new('inner1' => '', 'inner2' => 'value')
+        )
+      end
+
+      let(:result) do
+        document.compact_blank
+      end
+
+      it 'does not compact blank values in nested documents' do
+        expect(result['nested']['inner1']).to eq('')
+        expect(result['nested']['inner2']).to eq('value')
+      end
+
+      it 'preserves BSON::Document type for nested documents' do
+        expect(result['nested']).to be_a(described_class)
+      end
+    end
+  end
+
+  describe '#compact_blank!' do
+    let(:document) do
+      described_class.new(
+        'key1' => 'value1',
+        'key2' => '',
+        'key3' => nil,
+        'key4' => [],
+        'key5' => {}
+      )
+    end
+
+    context 'when changes are made' do
+      let(:result) do
+        document.compact_blank!
+      end
+
+      it 'returns self' do
+        expect(result).to be(document)
+      end
+
+      it 'removes blank values' do
+        result
+        expect(document.keys).to eq([ 'key1' ])
+        expect(document['key1']).to eq('value1')
+      end
+    end
+
+    context 'when no changes are made' do
+      let(:document) do
+        described_class.new('key1' => 'value1', 'key2' => 'value2')
+      end
+
+      let(:result) do
+        document.compact_blank!
+      end
+
+      it 'returns self' do
+        expect(result).to be(document)
       end
 
-      it 'raises ArgumentError' do
-        lambda do
-          doc.symbolize_keys!
-        end.should raise_error(ArgumentError, /symbolize_keys! is not supported on BSON::Document instances/)
+      it 'does not modify the original document' do
+        result
+        expect(document).to eq(described_class.new('key1' => 'value1', 'key2' => 'value2'))
       end
     end
   end
diff --git a/spec/bson/document_native_spec.rb b/spec/bson/document_native_spec.rb
new file mode 100644
index 000000000..4954fef05
--- /dev/null
+++ b/spec/bson/document_native_spec.rb
@@ -0,0 +1,2152 @@
+# frozen_string_literal: true
+
+# Copyright (C) 2009-2020 MongoDB Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+require 'spec_helper'
+
+# BSON::Document tests for native Hash method behaviors
+describe BSON::Document do
+  let(:document) do
+    described_class.new('key1' => 'value1', 'key2' => 'value2', 'key3' => 'value3')
+  end
+
+  describe '.try_convert' do
+    let(:object) do
+      { 'key1' => 'value1' }
+    end
+
+    let(:document) do
+      described_class.try_convert(object)
+    end
+
+    it 'converts the object to a document' do
+      expect(document).to be_a(described_class)
+      expect(document).to eq(described_class.new('key1' => 'value1'))
+    end
+
+    context 'when the object is contains a nested hash' do
+      let(:object) do
+        { 'key1' => 'value1', 'nested' => { 'key2' => 'value2' } }
+      end
+
+      it 'converts the nested hash to a document' do
+        nested = document['nested']
+        expect(nested).to be_a(described_class)
+        expect(nested).to eq(described_class.new('key2' => 'value2'))
+      end
+    end
+
+    context 'when the object is a BSON::Document' do
+      let(:object) do
+        described_class.new('key1' => 'value1')
+      end
+
+      it 'returns the document itself self' do
+        expect(document).to eq(object)
+      end
+    end
+
+    context 'when the object is not convertible to a hash' do
+      let(:object) do
+        'not a hash'
+      end
+
+      it 'returns nil' do
+        expect(document).to be_nil
+      end
+    end
+  end
+
+  describe '.[]' do
+    context 'with key-value pairs' do
+      let(:document) do
+        described_class['key1', 'value1', 'key2', 'value2']
+      end
+
+      it 'creates a document with the provided keys and values' do
+        expect(document).to be_a(described_class)
+        expect(document).to eq(described_class.new('key1' => 'value1', 'key2' => 'value2'))
+      end
+    end
+
+    context 'with a hash-like object' do
+      let(:hash) do
+        { 'key' => 'value' }
+      end
+
+      let(:document) do
+        described_class[hash]
+      end
+
+      it 'creates a document from the hash-like object' do
+        expect(document).to be_a(described_class)
+        expect(document).to eq(described_class.new('key' => 'value'))
+      end
+    end
+  end
+
+  describe '#to_h' do
+    context 'with a single-level document' do
+      let(:document) do
+        described_class.new('key1' => 'value1', 'key2' => 'value2')
+      end
+
+      let(:hash) do
+        document.to_h
+      end
+
+      it 'returns a Hash' do
+        expect(hash).to be_a(Hash)
+        expect(hash).not_to be_a(described_class)
+      end
+
+      it 'returns a hash with the same keys and values' do
+        expect(hash).to eq({ 'key1' => 'value1', 'key2' => 'value2' })
+      end
+    end
+
+    context 'with a nested document' do
+      let(:document) do
+        described_class.new('key1' => 'value1', 'key2' => described_class.new('key3' => 'value3'))
+      end
+
+      let(:hash) do
+        document.to_h
+      end
+
+      it 'does not convert nested documents to hashes' do
+        nested = hash['key2']
+        expect(nested).to be_a(described_class)
+      end
+
+      it 'preserves the nested structure' do
+        expect(hash).to eq({ 'key1' => 'value1', 'key2' => { 'key3' => 'value3' } })
+      end
+    end
+
+    context 'when a block is provided' do
+      let(:document) do
+        described_class.new('key1' => 'value1', 'key2' => 'value2')
+      end
+
+      let(:hash) do
+        document.to_h { |k, v| [ k.to_sym, v.upcase ] }
+      end
+
+      it 'returns a Hash' do
+        expect(hash).to be_a(Hash)
+        expect(hash).not_to be_a(described_class)
+      end
+
+      it 'applies the block to each key-value pair' do
+        expect(hash).to eq({ key1: 'VALUE1', key2: 'VALUE2' })
+      end
+    end
+
+    context 'with a static default' do
+      let(:document) do
+        doc = described_class.new('key1' => 'value1', 'key2' => 'value2')
+        doc.default = 'default_value'
+        doc
+      end
+
+      let(:hash) do
+        document.to_h
+      end
+
+      it 'returns a Hash' do
+        expect(hash).to be_a(Hash)
+        expect(hash).not_to be_a(described_class)
+      end
+
+      it 'returns a hash with the same keys and values' do
+        expect(hash).to eq({ 'key1' => 'value1', 'key2' => 'value2' })
+      end
+
+      it 'transfers the default value to the resulting hash' do
+        expect(hash.default).to eq('default_value')
+      end
+
+      it 'allows accessing the default with a non-existent key' do
+        expect(hash['non_existent']).to eq('default_value')
+      end
+    end
+
+    context 'with a default proc' do
+      let(:document) do
+        doc = described_class.new('key1' => 'value1', 'key2' => 'value2')
+        doc.default_proc = ->(_hash, key) { "default_for_#{key}" }
+        doc
+      end
+
+      let(:hash) do
+        document.to_h
+      end
+
+      it 'returns a Hash' do
+        expect(hash).to be_a(Hash)
+        expect(hash).not_to be_a(described_class)
+      end
+
+      it 'returns a hash with the same keys and values' do
+        expect(hash).to eq({ 'key1' => 'value1', 'key2' => 'value2' })
+      end
+
+      it 'transfers the default proc to the resulting hash' do
+        expect(hash.default_proc).not_to be_nil
+      end
+
+      it 'allows accessing the default with a non-existent key' do
+        expect(hash['non_existent']).to eq('default_for_non_existent')
+      end
+    end
+
+    context 'with both default and default_proc set' do
+      let(:document) do
+        doc = described_class.new('key1' => 'value1')
+        doc.default = 'default_value'
+        doc.default_proc = ->(_hash, key) { "proc_for_#{key}" }
+        doc
+      end
+
+      let(:hash) do
+        document.to_h
+      end
+
+      it 'preserves the most recently set default behavior' do
+        # Ruby's behavior is to use the most recently set default mechanism
+        expect(hash.default).to be_nil
+        expect(hash.default_proc).not_to be_nil
+        expect(hash['non_existent']).to eq('proc_for_non_existent')
+      end
+    end
+  end
+
+  describe '#to_hash' do
+    context 'with a single-level document' do
+      let(:document) do
+        described_class.new('key1' => 'value1', 'key2' => 'value2')
+      end
+
+      let(:hash) do
+        document.to_hash
+      end
+
+      it 'returns a Hash' do
+        expect(hash).to be_a(Hash)
+        expect(hash).not_to be_a(described_class)
+      end
+
+      it 'returns a hash with the same keys and values' do
+        expect(hash).to eq({ 'key1' => 'value1', 'key2' => 'value2' })
+      end
+    end
+
+    context 'with a nested document' do
+      let(:document) do
+        described_class.new('key1' => 'value1', 'key2' => described_class.new('key3' => 'value3'))
+      end
+
+      let(:hash) do
+        document.to_hash
+      end
+
+      it 'converts nested documents to hashes' do
+        nested = hash['key2']
+        expect(nested).to be_a(Hash)
+        expect(nested).not_to be_a(described_class)
+      end
+
+      it 'preserves the nested structure' do
+        expect(hash).to eq({ 'key1' => 'value1', 'key2' => { 'key3' => 'value3' } })
+      end
+    end
+
+    context 'with a static default' do
+      let(:document) do
+        doc = described_class.new('key1' => 'value1', 'key2' => 'value2')
+        doc.default = 'default_value'
+        doc
+      end
+
+      let(:hash) do
+        document.to_hash
+      end
+
+      it 'returns a Hash' do
+        expect(hash).to be_a(Hash)
+        expect(hash).not_to be_a(described_class)
+      end
+
+      it 'returns a hash with the same keys and values' do
+        expect(hash).to eq({ 'key1' => 'value1', 'key2' => 'value2' })
+      end
+
+      it 'transfers the default value to the resulting hash' do
+        expect(hash.default).to eq('default_value')
+      end
+
+      it 'allows accessing the default with a non-existent key' do
+        expect(hash['non_existent']).to eq('default_value')
+      end
+    end
+
+    context 'with a default proc' do
+      let(:document) do
+        doc = described_class.new('key1' => 'value1', 'key2' => 'value2')
+        doc.default_proc = ->(_hash, key) { "default_for_#{key}" }
+        doc
+      end
+
+      let(:hash) do
+        document.to_hash
+      end
+
+      it 'returns a Hash' do
+        expect(hash).to be_a(Hash)
+        expect(hash).not_to be_a(described_class)
+      end
+
+      it 'returns a hash with the same keys and values' do
+        expect(hash).to eq({ 'key1' => 'value1', 'key2' => 'value2' })
+      end
+
+      it 'transfers the default proc to the resulting hash' do
+        expect(hash.default_proc).not_to be_nil
+      end
+
+      it 'allows accessing the default with a non-existent key' do
+        expect(hash['non_existent']).to eq('default_for_non_existent')
+      end
+    end
+
+    context 'with a nested document with defaults' do
+      let(:nested_document) do
+        doc = described_class.new('inner' => 'value')
+        doc.default = 'inner_default'
+        doc
+      end
+
+      let(:document) do
+        doc = described_class.new('key1' => 'value1', 'nested' => nested_document)
+        doc.default = 'outer_default'
+        doc
+      end
+
+      let(:hash) do
+        document.to_hash
+      end
+
+      it 'converts nested documents to hashes' do
+        nested = hash['nested']
+        expect(nested).to be_a(Hash)
+        expect(nested).not_to be_a(described_class)
+      end
+
+      it 'preserves the nested structure' do
+        expect(hash).to eq({ 'key1' => 'value1', 'nested' => { 'inner' => 'value' } })
+      end
+
+      it 'transfers the default values appropriately' do
+        expect(hash.default).to eq('outer_default')
+        expect(hash['nested'].default).to eq('inner_default')
+      end
+
+      it 'allows accessing the defaults with non-existent keys' do
+        expect(hash['non_existent']).to eq('outer_default')
+        expect(hash['nested']['non_existent']).to eq('inner_default')
+      end
+    end
+
+    context 'with both default and default_proc set' do
+      let(:document) do
+        doc = described_class.new('key1' => 'value1')
+        doc.default = 'default_value'
+        doc.default_proc = ->(_hash, key) { "proc_for_#{key}" }
+        doc
+      end
+
+      let(:hash) do
+        document.to_hash
+      end
+
+      it 'preserves the most recently set default behavior' do
+        # Ruby's behavior is to use the most recently set default mechanism
+        expect(hash.default).to be_nil
+        expect(hash.default_proc).not_to be_nil
+        expect(hash['non_existent']).to eq('proc_for_non_existent')
+      end
+    end
+  end
+
+  describe '#[]=' do
+    context 'with string keys' do
+      let(:result) do
+        document['key4'] = 'value4'
+      end
+
+      it 'adds the key-value pair to the document' do
+        result
+        expect(document['key4']).to eq('value4')
+      end
+
+      it 'returns the value' do
+        expect(result).to eq('value4')
+      end
+    end
+
+    context 'with symbol keys' do
+      let(:result) do
+        document[:key4] = 'value4'
+      end
+
+      it 'adds the key-value pair with a string key' do
+        result
+        expect(document['key4']).to eq('value4')
+      end
+
+      it 'allows lookup with both string and symbol' do
+        result
+        expect(document[:key4]).to eq('value4')
+        expect(document['key4']).to eq('value4')
+      end
+    end
+
+    context 'with hash values' do
+      let(:result) do
+        document['nested'] = { 'inner' => 'value' }
+      end
+
+      it 'converts hash values to BSON::Document' do
+        result
+        expect(document['nested']).to be_a(described_class)
+        expect(document['nested']['inner']).to eq('value')
+      end
+    end
+
+    context 'with array values containing hashes' do
+      let(:result) do
+        document['array'] = [ 1, 2, { 'a' => 1 } ]
+      end
+
+      it 'converts hashes within arrays to BSON::Document' do
+        result
+        expect(document['array'][2]).to be_a(described_class)
+        expect(document['array'][2]['a']).to eq(1)
+      end
+    end
+
+    context 'when overwriting an existing key' do
+      let(:result) do
+        document['key1'] = 'new_value'
+      end
+
+      it 'replaces the value for the key' do
+        result
+        expect(document['key1']).to eq('new_value')
+      end
+
+      it 'does not change the order of keys' do
+        result
+        expect(document.keys).to eq(%w[key1 key2 key3])
+      end
+    end
+
+    context 'with nested documents' do
+      let(:nested_doc) do
+        described_class.new('inner' => 'value')
+      end
+
+      let(:result) do
+        document['nested'] = nested_doc
+      end
+
+      it 'preserves BSON::Document values' do
+        result
+        expect(document['nested']).to be(nested_doc)
+        expect(document['nested']).to be_a(described_class)
+      end
+    end
+  end
+
+  describe '#store' do
+    it 'is an alias for []=' do
+      expect(document.method(:store)).to eq(document.method(:[]=))
+    end
+  end
+
+  describe '#has_key?' do
+    context 'with existing string keys' do
+      it 'returns true' do
+        expect(document.key?('key1')).to be true
+      end
+    end
+
+    context 'with existing symbol keys' do
+      it 'returns true' do
+        expect(document.key?(:key1)).to be true
+      end
+    end
+
+    context 'with non-existent keys' do
+      it 'returns false' do
+        expect(document.key?('non_existent')).to be false
+      end
+    end
+  end
+
+  describe '#include?' do
+    it 'is an alias for has_key?' do
+      expect(document.method(:include?)).to eq(document.method(:has_key?))
+    end
+  end
+
+  describe '#key?' do
+    it 'is an alias for has_key?' do
+      expect(document.method(:key?)).to eq(document.method(:has_key?))
+    end
+  end
+
+  describe '#member?' do
+    it 'is an alias for has_key?' do
+      expect(document.method(:member?)).to eq(document.method(:has_key?))
+    end
+  end
+
+  describe '#key' do
+    context 'with existing values' do
+      let(:result) do
+        document.key('value1')
+      end
+
+      it 'returns the key for the value' do
+        expect(result).to eq('key1')
+      end
+    end
+
+    context 'with multiple matching values' do
+      let(:document_with_duplicates) do
+        described_class.new('key1' => 'duplicate', 'key2' => 'duplicate')
+      end
+
+      let(:result) do
+        document_with_duplicates.key('duplicate')
+      end
+
+      it 'returns the first matching key' do
+        expect(result).to eq('key1')
+      end
+    end
+
+    context 'with non-existent values' do
+      let(:result) do
+        document.key('non_existent')
+      end
+
+      it 'returns nil for non-existent values' do
+        expect(result).to be_nil
+      end
+    end
+
+    context 'with symbol values' do
+      let(:document_with_symbols) do
+        described_class.new('key1' => :symbol_value)
+      end
+
+      let(:result) do
+        document_with_symbols.key(:symbol_value)
+      end
+
+      it 'converts symbol values correctly' do
+        expect(result).to eq('key1')
+      end
+    end
+
+    context 'with nested document values' do
+      let(:nested_doc) do
+        described_class.new('inner' => 'value')
+      end
+
+      let(:document_with_nested) do
+        described_class.new('key1' => nested_doc)
+      end
+
+      let(:result) do
+        document_with_nested.key(nested_doc)
+      end
+
+      it 'can find BSON::Document values' do
+        expect(result).to eq('key1')
+      end
+
+      context 'when searching with an equivalent hash' do
+        let(:result) do
+          document_with_nested.key({ 'inner' => 'value' })
+        end
+
+        it 'finds the key by equivalent hash' do
+          expect(result).to eq('key1')
+        end
+      end
+    end
+  end
+
+  describe '#default' do
+    context 'without default value' do
+      let(:default) do
+        document.default
+      end
+
+      it 'returns nil' do
+        expect(default).to be_nil
+      end
+    end
+
+    context 'with default value' do
+      let(:document_with_default) do
+        doc = described_class.new('key1' => 'value1')
+        doc.default = 'default_value'
+        doc
+      end
+
+      let(:default) do
+        document_with_default.default
+      end
+
+      it 'returns the default value' do
+        expect(default).to eq('default_value')
+      end
+    end
+
+    context 'with default proc' do
+      let(:document_with_default_proc) do
+        doc = described_class.new('key1' => 'value1')
+        doc.default_proc = ->(_hash, key) { "default_for_#{key}" }
+        doc
+      end
+
+      let(:default) do
+        document_with_default_proc.default('missing')
+      end
+
+      it 'returns the processed default value' do
+        expect(default).to eq('default_for_missing')
+      end
+    end
+  end
+
+  describe '#default=' do
+    let(:document_with_default) do
+      doc = described_class.new('key1' => 'value1')
+      doc.default = 'default_value'
+      doc
+    end
+
+    it 'sets the default value' do
+      expect(document_with_default.default).to eq('default_value')
+    end
+
+    it 'returns the default value for missing keys' do
+      expect(document_with_default['missing']).to eq('default_value')
+    end
+  end
+
+  describe '#has_value?' do
+    context 'with existing values' do
+      it 'returns true' do
+        expect(document.value?('value1')).to be true
+      end
+    end
+
+    context 'with symbol values' do
+      let(:document_with_symbols) do
+        described_class.new('key1' => :symbol_value)
+      end
+
+      it 'returns true when searching with a symbol' do
+        expect(document_with_symbols.value?(:symbol_value)).to be true
+      end
+    end
+
+    context 'with non-existent values' do
+      it 'returns false' do
+        expect(document.value?('non_existent')).to be false
+      end
+    end
+  end
+
+  describe '#value?' do
+    it 'is an alias for has_value?' do
+      expect(document.method(:value?)).to eq(document.method(:has_value?))
+    end
+  end
+
+  describe '#values_at' do
+    context 'with string keys' do
+      let(:values) do
+        document.values_at('key1', 'key3')
+      end
+
+      it 'returns the values for the keys' do
+        expect(values).to eq(%w[value1 value3])
+      end
+    end
+
+    context 'with symbol keys' do
+      let(:values) do
+        document.values_at(:key1, :key3)
+      end
+
+      it 'returns the values for the keys' do
+        expect(values).to eq(%w[value1 value3])
+      end
+    end
+
+    context 'with missing keys' do
+      let(:values) do
+        document.values_at('key1', 'missing')
+      end
+
+      it 'returns nil for missing keys' do
+        expect(values).to eq([ 'value1', nil ])
+      end
+    end
+
+    context 'with nested documents' do
+      let(:document) do
+        described_class.new(
+          'key1' => 'value1',
+          'nested' => described_class.new('inner1' => 'nested_value1', 'inner2' => 'nested_value2')
+        )
+      end
+
+      let(:values) do
+        document.values_at('key1', 'nested')
+      end
+
+      it 'returns the values for the keys' do
+        expect(values[0]).to eq('value1')
+        expect(values[1]).to be_a(described_class)
+        expect(values[1]['inner1']).to eq('nested_value1')
+      end
+    end
+  end
+
+  describe '#assoc' do
+    context 'with string keys' do
+      let(:pair) do
+        document.assoc('key1')
+      end
+
+      it 'returns the key-value pair' do
+        expect(pair).to eq(%w[key1 value1])
+      end
+    end
+
+    context 'with symbol keys' do
+      let(:pair) do
+        document.assoc(:key1)
+      end
+
+      it 'returns the key-value pair' do
+        expect(pair).to eq(%w[key1 value1])
+      end
+    end
+
+    context 'with missing keys' do
+      let(:pair) do
+        document.assoc('missing')
+      end
+
+      it 'returns nil for missing keys' do
+        expect(pair).to be_nil
+      end
+    end
+  end
+
+  describe '#rassoc' do
+    context 'with existing values' do
+      let(:result) do
+        document.rassoc('value1')
+      end
+
+      it 'returns the key-value pair' do
+        expect(result).to eq(%w[key1 value1])
+      end
+    end
+
+    context 'with multiple matching values' do
+      let(:document_with_duplicates) do
+        described_class.new('key1' => 'duplicate', 'key2' => 'duplicate')
+      end
+
+      let(:result) do
+        document_with_duplicates.rassoc('duplicate')
+      end
+
+      it 'returns the first matching pair' do
+        expect(result).to eq(%w[key1 duplicate])
+      end
+    end
+
+    context 'with non-existent values' do
+      let(:result) do
+        document.rassoc('non_existent')
+      end
+
+      it 'returns nil for non-existent values' do
+        expect(result).to be_nil
+      end
+    end
+
+    context 'with symbol values' do
+      let(:document_with_symbols) do
+        described_class.new('key1' => :symbol_value)
+      end
+
+      context 'when searching with a symbol' do
+        let(:result) do
+          document_with_symbols.rassoc(:symbol_value)
+        end
+
+        it 'finds the key-value pair' do
+          expect(result).to eq([ 'key1', :symbol_value ])
+        end
+      end
+
+      context 'when searching with a string' do
+        let(:result) do
+          document_with_symbols.rassoc('symbol_value')
+        end
+
+        it 'does not find the key-value pair' do
+          expect(result).to be_nil
+        end
+      end
+    end
+
+    context 'with nested document values' do
+      let(:nested_doc) do
+        described_class.new('inner' => 'value')
+      end
+
+      let(:document_with_nested) do
+        described_class.new('key1' => nested_doc)
+      end
+
+      let(:result) do
+        document_with_nested.rassoc(nested_doc)
+      end
+
+      it 'can find BSON::Document values' do
+        expect(result).to eq([ 'key1', nested_doc ])
+      end
+
+      context 'when searching with an equivalent hash' do
+        let(:result) do
+          document_with_nested.rassoc({ 'inner' => 'value' })
+        end
+
+        it 'finds the pair by equivalent hash' do
+          expect(result).to eq([ 'key1', { 'inner' => 'value' } ])
+        end
+      end
+    end
+  end
+
+  describe '#fetch_values' do
+    context 'with string keys' do
+      let(:values) do
+        document.fetch_values('key1', 'key3')
+      end
+
+      it 'returns the values for the keys' do
+        expect(values).to eq(%w[value1 value3])
+      end
+    end
+
+    context 'with symbol keys' do
+      let(:values) do
+        document.fetch_values(:key1, :key3)
+      end
+
+      it 'returns the values for the keys' do
+        expect(values).to eq(%w[value1 value3])
+      end
+    end
+
+    context 'with missing keys and no block' do
+      it 'raises KeyError for missing keys' do
+        expect do
+          document.fetch_values('key1', 'missing')
+        end.to raise_error(KeyError)
+      end
+    end
+
+    context 'with missing keys and a block' do
+      let(:values) do
+        document.fetch_values('key1', 'missing') { |key| "default_for_#{key}" }
+      end
+
+      it 'uses the block for missing keys' do
+        expect(values).to eq(%w[value1 default_for_missing])
+      end
+    end
+  end
+
+  describe '#invert' do
+    let(:document) do
+      described_class.new('key1' => 'value1', 'key2' => 'value2')
+    end
+
+    let(:inverted) do
+      document.invert
+    end
+
+    it 'returns a new BSON::Document' do
+      expect(inverted).to be_a(described_class)
+      expect(inverted).not_to be(document)
+    end
+
+    it 'inverts keys and values' do
+      expect(inverted).to eq(described_class.new('value1' => 'key1', 'value2' => 'key2'))
+    end
+
+    context 'with nested documents' do
+      let(:document) do
+        described_class.new('key1' => 'value1', 'key2' => described_class.new('nested' => 'value2'))
+      end
+
+      let(:inverted) do
+        document.invert
+      end
+
+      let(:nested_key) do
+        inverted.keys.detect { |k| k.include?('nested') }
+      end
+
+      it 'does convert nested documents' do
+        expect(nested_key).to be_a(described_class)
+        expect(nested_key).to eq(document['key2'])
+      end
+
+      it 'does not attempt to invert nested documents recursively' do
+        expect(inverted[nested_key]).to eq('key2')
+      end
+    end
+  end
+
+  describe '#rehash' do
+    let(:document) do
+      described_class.new('key1' => 'value1', 'key2' => 'value2')
+    end
+
+    it 'returns self' do
+      expect(document.rehash).to be(document)
+    end
+
+    context 'with mutable keys' do
+      let(:mutable_key) do
+        { id: 1 }
+      end
+
+      let(:document) do
+        described_class.new(mutable_key => 'value')
+      end
+
+      before do
+        mutable_key[:id] = 2
+      end
+
+      it 'rebuilds hash index after key changes' do
+        expect { document.rehash }.not_to raise_error
+        expect(document.keys.first).to eq({ id: 2 })
+      end
+    end
+  end
+
+  describe '#delete' do
+    let(:document) do
+      described_class.new('key1' => 'value1', 'key2' => 'value2')
+    end
+
+    context 'when the key exists' do
+      it 'returns the value' do
+        expect(document.delete('key1')).to eq('value1')
+      end
+
+      it 'removes the key-value pair' do
+        document.delete('key1')
+        expect(document).to eq(described_class.new('key2' => 'value2'))
+      end
+    end
+
+    context 'when the key is a symbol' do
+      let(:document) do
+        described_class.new(key1: 'value1', 'key2' => 'value2')
+      end
+
+      it 'returns the value' do
+        expect(document.delete(:key1)).to eq('value1')
+      end
+
+      it 'removes the key-value pair' do
+        document.delete(:key1)
+        expect(document).to eq(described_class.new('key2' => 'value2'))
+      end
+    end
+
+    context 'when the key does not exist' do
+      it 'returns nil' do
+        expect(document.delete('nonexistent')).to be_nil
+      end
+    end
+
+    context 'when a block is provided' do
+      let(:value) do
+        document.delete('key1') { |key| "default for #{key}" }
+      end
+
+      it 'returns the result of the block' do
+        expect(value).to eq('value1')
+      end
+    end
+
+    context 'when a block is provided and the key does not exist' do
+      let(:value) do
+        document.delete('nonexistent') { |key| "default for #{key}" }
+      end
+
+      it 'returns the result of the block' do
+        expect(value).to eq('default for nonexistent')
+      end
+    end
+  end
+
+  describe '#clear' do
+    let(:document) do
+      described_class.new('key1' => 'value1', 'key2' => 'value2')
+    end
+
+    let(:result) do
+      document.clear
+    end
+
+    it 'returns self' do
+      expect(result).to be(document)
+    end
+
+    it 'removes all key-value pairs' do
+      result
+      expect(document).to be_empty
+    end
+  end
+
+  describe '#shift' do
+    let(:document) do
+      described_class.new('key1' => 'value1', 'key2' => 'value2')
+    end
+
+    let(:pair) do
+      document.shift
+    end
+
+    it 'returns the first key-value pair as an array' do
+      expect(pair).to eq(%w[key1 value1])
+    end
+
+    it 'removes the first key-value pair from the document' do
+      document.shift
+      expect(document).to eq(described_class.new('key2' => 'value2'))
+    end
+
+    context 'when the document is empty' do
+      let(:empty_document) do
+        described_class.new
+      end
+
+      it 'returns nil' do
+        expect(empty_document.shift).to be_nil
+      end
+    end
+  end
+
+  describe '#merge' do
+    let(:document) do
+      described_class.new('key1' => 'value1', 'key2' => 'value2')
+    end
+
+    context 'when merging with another document' do
+      let(:other) do
+        described_class.new('key2' => 'new_value', 'key3' => 'value3')
+      end
+
+      let(:result) do
+        document.merge(other)
+      end
+
+      it 'returns a new BSON::Document' do
+        expect(result).to be_a(described_class)
+        expect(result).not_to be(document)
+      end
+
+      it 'includes all keys from both documents' do
+        expect(result.keys).to include('key1', 'key2', 'key3')
+      end
+
+      it 'uses values from the other document for duplicate keys' do
+        expect(result['key2']).to eq('new_value')
+      end
+    end
+
+    context 'when merging with a hash' do
+      let(:other) do
+        { 'key2' => 'new_value', 'key3' => 'value3' }
+      end
+
+      let(:result) do
+        document.merge(other)
+      end
+
+      it 'returns a BSON::Document' do
+        expect(result).to be_a(described_class)
+      end
+
+      it 'includes all keys from both documents' do
+        expect(result.keys).to include('key1', 'key2', 'key3')
+      end
+    end
+
+    context 'when a block is provided' do
+      let(:other) do
+        { 'key1' => 'other_value', 'key3' => 'value3' }
+      end
+
+      let(:result) do
+        document.merge(other) do |_key, old_val, new_val|
+          "#{old_val} and #{new_val}"
+        end
+      end
+
+      it 'uses the result of the block for duplicate keys' do
+        expect(result['key1']).to eq('value1 and other_value')
+      end
+
+      it 'uses the value of the other hash for non-duplicate keys' do
+        expect(result['key3']).to eq('value3')
+      end
+    end
+
+    context 'with nested documents' do
+      let(:document) do
+        described_class.new('key1' => 'value1', 'nested' => described_class.new('a' => 1, 'b' => 2))
+      end
+
+      let(:other) do
+        { 'key2' => 'value2', 'nested' => { 'b' => 3, 'c' => 4 } }
+      end
+
+      let(:result) do
+        document.merge(other)
+      end
+
+      it 'replaces the nested document' do
+        expect(result['nested']).to eq(described_class.new('b' => 3, 'c' => 4))
+      end
+
+      it 'returns nested BSON::Document' do
+        expect(result['nested']).to be_a(described_class)
+      end
+    end
+  end
+
+  describe '#merge!' do
+    let(:document) do
+      described_class.new('key1' => 'value1', 'key2' => 'value2')
+    end
+
+    context 'when merging with another document' do
+      let(:other) do
+        described_class.new('key2' => 'new_value', 'key3' => 'value3')
+      end
+
+      let(:result) do
+        document.merge!(other)
+      end
+
+      it 'returns self' do
+        expect(result).to be(document)
+      end
+
+      it 'modifies the original document' do
+        result
+        expect(document['key2']).to eq('new_value')
+        expect(document['key3']).to eq('value3')
+      end
+    end
+
+    context 'when merging with a hash' do
+      let(:other) do
+        { 'key2' => 'new_value', 'key3' => 'value3' }
+      end
+
+      let(:result) do
+        document.merge!(other)
+      end
+
+      it 'returns self' do
+        expect(result).to be(document)
+      end
+
+      it 'modifies the original document' do
+        result
+        expect(document['key2']).to eq('new_value')
+        expect(document['key3']).to eq('value3')
+      end
+    end
+
+    context 'when a block is provided' do
+      let(:other) do
+        { 'key1' => 'other_value', 'key3' => 'value3' }
+      end
+
+      let(:result) do
+        document.merge!(other) do |_key, old_val, new_val|
+          "#{old_val} and #{new_val}"
+        end
+      end
+
+      it 'uses the result of the block for duplicate keys' do
+        result
+        expect(document['key1']).to eq('value1 and other_value')
+      end
+
+      it 'uses the value of the other hash for non-duplicate keys' do
+        result
+        expect(document['key3']).to eq('value3')
+      end
+    end
+
+    context 'with nested documents' do
+      let(:document) do
+        described_class.new('key1' => 'value1', 'nested' => described_class.new('a' => 1, 'b' => 2))
+      end
+
+      let(:other) do
+        { 'key2' => 'value2', 'nested' => { 'b' => 3, 'c' => 4 } }
+      end
+
+      let(:result) do
+        document.merge!(other)
+      end
+
+      it 'replaces the nested document' do
+        result
+        expect(document['nested']).to eq(described_class.new('b' => 3, 'c' => 4))
+      end
+
+      it 'converts the nested hash to a BSON::Document' do
+        result
+        expect(document['nested']).to be_a(described_class)
+      end
+    end
+  end
+
+  describe '#update' do
+    let(:document) do
+      described_class.new('key1' => 'value1')
+    end
+
+    let(:other) do
+      { 'key2' => 'value2' }
+    end
+
+    it 'is an alias for merge!' do
+      expect(document.method(:update)).to eq(document.method(:merge!))
+    end
+
+    it 'updates the document in place' do
+      document.update(other)
+      expect(document).to eq(described_class.new('key1' => 'value1', 'key2' => 'value2'))
+    end
+  end
+
+  describe '#reject' do
+    let(:result) do
+      document.reject { |k, v| k == 'key1' || v == 'value3' }
+    end
+
+    it 'returns a new BSON::Document' do
+      expect(result).to be_a(described_class)
+      expect(result).not_to be(document)
+    end
+
+    it 'excludes keys for which the block returns true' do
+      expect(result).to eq(described_class.new('key2' => 'value2'))
+    end
+
+    it 'does not modify the original document' do
+      result
+      expect(document).to eq(described_class.new('key1' => 'value1', 'key2' => 'value2', 'key3' => 'value3'))
+    end
+
+    context 'when no changes are made' do
+      let(:result) do
+        document.reject { |_k, _v| false }
+      end
+
+      it 'returns a new BSON::Document' do
+        expect(result).to be_a(described_class)
+        expect(result).not_to be(document)
+      end
+
+      it 'returns all original keys and values' do
+        expect(result).to eq(described_class.new('key1' => 'value1', 'key2' => 'value2', 'key3' => 'value3'))
+      end
+
+      it 'does not modify the original document' do
+        result
+        expect(document).to eq(described_class.new('key1' => 'value1', 'key2' => 'value2', 'key3' => 'value3'))
+      end
+    end
+
+    context 'when block not given' do
+      let(:enumerator) do
+        document.reject
+      end
+
+      it 'returns an enumerator' do
+        expect(enumerator).to be_a(Enumerator)
+      end
+
+      it 'enumerates over all key-value pairs' do
+        pairs = enumerator.to_a
+        expect(pairs.length).to eq(document.length)
+        expect(pairs.map(&:first)).to eq(document.keys)
+        expect(pairs.map(&:last)).to eq(document.values)
+      end
+
+      it 'produces a BSON::Document when used with a block' do
+        result = enumerator.each { |key, value| key == 'key1' || value == 'value3' }
+        expect(result).to be_a(described_class)
+        expect(result).to eq(described_class.new('key2' => 'value2'))
+      end
+    end
+  end
+
+  describe '#reject!' do
+    context 'when changes are made' do
+      let(:result) do
+        document.reject! { |k, v| k == 'key1' || v == 'value3' }
+      end
+
+      it 'returns self' do
+        expect(result).to be(document)
+      end
+
+      it 'modifies the original document' do
+        result
+        expect(document).to eq(described_class.new('key2' => 'value2'))
+      end
+    end
+
+    context 'when no changes are made' do
+      let(:result) do
+        document.reject! { |_k, _v| false }
+      end
+
+      it 'returns nil' do
+        expect(result).to be_nil
+      end
+
+      it 'does not modify the original document' do
+        result
+        expect(document).to eq(described_class.new('key1' => 'value1', 'key2' => 'value2', 'key3' => 'value3'))
+      end
+    end
+
+    context 'when block not given' do
+      let(:enumerator) do
+        document.dup.reject!
+      end
+
+      it 'returns an enumerator' do
+        expect(enumerator).to be_a(Enumerator)
+      end
+
+      it 'enumerates over all key-value pairs' do
+        pairs = enumerator.to_a
+        expect(pairs.length).to eq(document.length)
+        expect(pairs.map(&:first)).to eq(document.keys)
+        expect(pairs.map(&:last)).to eq(document.values)
+      end
+
+      it 'modifies the original document when used with a block' do
+        result = document.reject!.each { |key, value| key == 'key1' || value == 'value3' }
+        expect(result).to be(document)
+        expect(document).to eq(described_class.new('key2' => 'value2'))
+      end
+
+      it 'returns nil if no changes are made' do
+        result = document.reject!.each { |_key, _value| false } # rubocop:disable Lint/Void
+        expect(result).to be_nil
+        expect(document).to eq(described_class.new('key1' => 'value1', 'key2' => 'value2', 'key3' => 'value3'))
+      end
+    end
+  end
+
+  describe '#delete_if' do
+    context 'when changes are made' do
+      let(:result) do
+        document.delete_if { |k, v| k == 'key1' || v == 'value3' }
+      end
+
+      it 'returns self' do
+        expect(result).to be(document)
+      end
+
+      it 'modifies the original document' do
+        result
+        expect(document).to eq(described_class.new('key2' => 'value2'))
+      end
+    end
+
+    context 'when no changes are made' do
+      let(:result) do
+        document.delete_if { |_k, _v| false }
+      end
+
+      it 'returns nil' do
+        expect(result).to be(document)
+      end
+
+      it 'does not modify the original document' do
+        result
+        expect(document).to eq(described_class.new('key1' => 'value1', 'key2' => 'value2', 'key3' => 'value3'))
+      end
+    end
+
+    context 'when block not given' do
+      let(:enumerator) do
+        document.dup.delete_if
+      end
+
+      it 'returns an enumerator' do
+        expect(enumerator).to be_a(Enumerator)
+      end
+
+      it 'enumerates over all key-value pairs' do
+        pairs = enumerator.to_a
+        expect(pairs.length).to eq(document.length)
+        expect(pairs.map(&:first)).to eq(document.keys)
+        expect(pairs.map(&:last)).to eq(document.values)
+      end
+
+      it 'modifies the original document when used with a block' do
+        result = document.delete_if.each { |key, value| key == 'key1' || value == 'value3' }
+        expect(result).to be(document)
+        expect(document).to eq(described_class.new('key2' => 'value2'))
+      end
+
+      it 'returns self if no changes are made' do
+        result = document.delete_if.each { |_key, _value| false } # rubocop:disable Lint/Void
+        expect(result).to be(document)
+      end
+    end
+  end
+
+  describe '#select' do
+    let(:result) do
+      document.select { |k, v| k == 'key1' || v == 'value3' }
+    end
+
+    it 'returns a new BSON::Document' do
+      expect(result).to be_a(described_class)
+      expect(result).not_to be(document)
+    end
+
+    it 'includes keys for which the block returns true' do
+      expect(result).to eq(described_class.new('key1' => 'value1', 'key3' => 'value3'))
+    end
+
+    it 'does not modify the original document' do
+      result
+      expect(document).to eq(described_class.new('key1' => 'value1', 'key2' => 'value2', 'key3' => 'value3'))
+    end
+
+    context 'when no changes are made' do
+      let(:result) do
+        document.select { |_k, _v| true }
+      end
+
+      it 'returns a new BSON::Document' do
+        expect(result).to be_a(described_class)
+        expect(result).not_to be(document)
+      end
+
+      it 'returns all original keys and values' do
+        expect(result).to eq(described_class.new('key1' => 'value1', 'key2' => 'value2', 'key3' => 'value3'))
+      end
+
+      it 'does not modify the original document' do
+        result
+        expect(document).to eq(described_class.new('key1' => 'value1', 'key2' => 'value2', 'key3' => 'value3'))
+      end
+    end
+
+    context 'when block not given' do
+      let(:enumerator) do
+        document.select
+      end
+
+      it 'returns an enumerator' do
+        expect(enumerator).to be_a(Enumerator)
+      end
+
+      it 'enumerates over all key-value pairs' do
+        pairs = enumerator.to_a
+        expect(pairs.length).to eq(document.length)
+        expect(pairs.map(&:first)).to eq(document.keys)
+        expect(pairs.map(&:last)).to eq(document.values)
+      end
+
+      it 'produces a BSON::Document when used with a block' do
+        result = enumerator.each { |key, value| key == 'key1' || value == 'value3' }
+        expect(result).to be_a(described_class)
+        expect(result).to eq(described_class.new('key1' => 'value1', 'key3' => 'value3'))
+      end
+    end
+  end
+
+  describe '#select!' do
+    context 'when changes are made' do
+      let(:result) do
+        document.select! { |k, v| k == 'key1' || v == 'value3' }
+      end
+
+      it 'returns self' do
+        expect(result).to be(document)
+      end
+
+      it 'modifies the original document' do
+        result
+        expect(document).to eq(described_class.new('key1' => 'value1', 'key3' => 'value3'))
+      end
+    end
+
+    context 'when no changes are made' do
+      let(:result) do
+        document.select! { |_k, _v| true }
+      end
+
+      it 'returns nil' do
+        expect(result).to be_nil
+      end
+
+      it 'does not modify the original document' do
+        result
+        expect(document).to eq(described_class.new('key1' => 'value1', 'key2' => 'value2', 'key3' => 'value3'))
+      end
+    end
+
+    context 'when block not given' do
+      let(:enumerator) do
+        document.dup.select!
+      end
+
+      it 'returns an enumerator' do
+        expect(enumerator).to be_a(Enumerator)
+      end
+
+      it 'enumerates over all key-value pairs' do
+        pairs = enumerator.to_a
+        expect(pairs.length).to eq(document.length)
+        expect(pairs.map(&:first)).to eq(document.keys)
+        expect(pairs.map(&:last)).to eq(document.values)
+      end
+
+      it 'modifies the original document when used with a block' do
+        result = document.select!.each { |key, value| key == 'key1' || value == 'value3' }
+        expect(result).to be(document)
+        expect(document).to eq(described_class.new('key1' => 'value1', 'key3' => 'value3'))
+      end
+
+      it 'returns nil if no changes are made' do
+        result = document.select!.each { |_key, _value| true } # rubocop:disable Lint/Void
+        expect(result).to be_nil
+        expect(document).to eq('key1' => 'value1', 'key2' => 'value2', 'key3' => 'value3')
+      end
+    end
+  end
+
+  describe '#filter' do
+    it 'is an alias for select' do
+      expect(document.method(:filter)).to eq(document.method(:select))
+    end
+
+    context 'when block not given' do
+      let(:enumerator) do
+        document.filter
+      end
+
+      it 'is an alias for select' do
+        expect(document.method(:filter)).to eq(document.method(:select))
+      end
+
+      it 'returns an enumerator' do
+        expect(enumerator).to be_a(Enumerator)
+      end
+
+      it 'produces a BSON::Document when used with a block' do
+        result = enumerator.each { |key, value| key == 'key1' || value == 'value3' }
+        expect(result).to be_a(described_class)
+        expect(result).to eq(described_class.new('key1' => 'value1', 'key3' => 'value3'))
+      end
+    end
+  end
+
+  describe '#filter!' do
+    it 'is an alias for select!' do
+      expect(document.method(:filter!)).to eq(document.method(:select!))
+    end
+  end
+
+  describe '#keep_if' do
+    context 'when changes are made' do
+      let(:result) do
+        document.keep_if { |k, v| k == 'key1' || v == 'value3' }
+      end
+
+      it 'returns self' do
+        expect(result).to be(document)
+      end
+
+      it 'modifies the original document' do
+        result
+        expect(document).to eq(described_class.new('key1' => 'value1', 'key3' => 'value3'))
+      end
+    end
+
+    context 'when no changes are made' do
+      let(:result) do
+        document.keep_if { |_k, _v| true }
+      end
+
+      it 'returns self' do
+        expect(result).to be(document)
+      end
+
+      it 'does not modify the original document' do
+        result
+        expect(document).to eq(described_class.new('key1' => 'value1', 'key2' => 'value2', 'key3' => 'value3'))
+      end
+    end
+
+    context 'when block not given' do
+      let(:enumerator) do
+        document.dup.keep_if
+      end
+
+      it 'returns an enumerator' do
+        expect(enumerator).to be_a(Enumerator)
+      end
+
+      it 'enumerates over all key-value pairs' do
+        pairs = enumerator.to_a
+        expect(pairs.length).to eq(document.length)
+        expect(pairs.map(&:first)).to eq(document.keys)
+        expect(pairs.map(&:last)).to eq(document.values)
+      end
+
+      it 'modifies the original document when used with a block' do
+        result = document.keep_if.each { |key, value| key == 'key1' || value == 'value3' }
+        expect(result).to be(document)
+        expect(document).to eq(described_class.new('key1' => 'value1', 'key3' => 'value3'))
+      end
+
+      it 'returns self if no changes are made' do
+        result = document.keep_if.each { |_key, _value| true } # rubocop:disable Lint/Void
+        expect(result).to eq(document)
+      end
+    end
+  end
+
+  describe '#compact' do
+    let(:document) do
+      described_class.new('key1' => 'value1', 'key2' => nil, 'key3' => 'value3')
+    end
+
+    let(:result) do
+      document.compact
+    end
+
+    it 'returns a new BSON::Document' do
+      expect(result).to be_a(described_class)
+      expect(result).not_to be(document)
+    end
+
+    it 'excludes pairs with nil values' do
+      expect(result).to eq(described_class.new('key1' => 'value1', 'key3' => 'value3'))
+    end
+
+    it 'does not modify the original document' do
+      result
+      expect(document).to eq(described_class.new('key1' => 'value1', 'key2' => nil, 'key3' => 'value3'))
+    end
+  end
+
+  describe '#compact!' do
+    let(:document) do
+      described_class.new('key1' => 'value1', 'key2' => nil, 'key3' => 'value3')
+    end
+
+    context 'when there are nil values' do
+      let(:result) do
+        document.compact!
+      end
+
+      it 'returns self' do
+        expect(result).to be(document)
+      end
+
+      it 'modifies the original document' do
+        result
+        expect(document).to eq(described_class.new('key1' => 'value1', 'key3' => 'value3'))
+      end
+    end
+
+    context 'when there are no nil values' do
+      let(:document) do
+        described_class.new('key1' => 'value1', 'key3' => 'value3')
+      end
+
+      let(:result) do
+        document.compact!
+      end
+
+      it 'returns nil' do
+        expect(result).to be_nil
+      end
+
+      it 'does not modify the original document' do
+        result
+        expect(document).to eq(described_class.new('key1' => 'value1', 'key3' => 'value3'))
+      end
+    end
+  end
+
+  describe '#slice' do
+    context 'with a single-level document' do
+      let(:result) do
+        document.slice('key1', 'key3')
+      end
+
+      it 'returns a new BSON::Document' do
+        expect(result).to be_a(described_class)
+        expect(result).not_to be(document)
+      end
+
+      it 'includes only the specified keys' do
+        expect(result).to eq(described_class.new('key1' => 'value1', 'key3' => 'value3'))
+      end
+
+      it 'does not modify the original document' do
+        result
+        expect(document).to eq(described_class.new('key1' => 'value1', 'key2' => 'value2', 'key3' => 'value3'))
+      end
+    end
+
+    context 'when some keys do not exist' do
+      let(:document) do
+        described_class.new('key1' => 'value1', 'key2' => 'value2')
+      end
+
+      let(:result) do
+        document.slice('key1', 'nonexistent')
+      end
+
+      it 'includes only the existing keys' do
+        expect(result).to eq(described_class.new('key1' => 'value1'))
+      end
+    end
+
+    context 'with symbol keys' do
+      let(:document) do
+        described_class.new(key1: 'value1', key2: 'value2')
+      end
+
+      let(:result) do
+        document.slice(:key1)
+      end
+
+      it 'handles symbol keys correctly' do
+        expect(result).to eq(described_class.new('key1' => 'value1'))
+      end
+    end
+  end
+
+  describe '#transform_keys' do
+    let(:result) do
+      document.transform_keys(&:upcase)
+    end
+
+    it 'returns a new BSON::Document' do
+      expect(result).to be_a(described_class)
+      expect(result).not_to be(document)
+    end
+
+    it 'transforms all keys according to the block' do
+      expect(result).to eq({ 'KEY1' => 'value1', 'KEY2' => 'value2', 'KEY3' => 'value3' })
+    end
+
+    it 'does not modify the original document' do
+      result
+      expect(document).to eq(described_class.new('key1' => 'value1', 'key2' => 'value2', 'key3' => 'value3'))
+    end
+
+    context 'with nested documents' do
+      let(:document) do
+        described_class.new('outer' => described_class.new('inner' => 'value'))
+      end
+
+      let(:result) do
+        document.transform_keys(&:upcase)
+      end
+
+      it 'does not transform keys in nested documents' do
+        expect(result).to eq({ 'OUTER' => { 'inner' => 'value' } })
+      end
+
+      it 'keeps nested elements as BSON::Document' do
+        expect(result['OUTER']).to be_a(described_class)
+      end
+    end
+
+    context 'when block not given' do
+      let(:enumerator) do
+        document.transform_keys
+      end
+
+      it 'returns an enumerator' do
+        expect(enumerator).to be_a(Enumerator)
+      end
+
+      it 'enumerates over all keys' do
+        expect(enumerator.to_a).to eq(document.keys)
+      end
+
+      it 'produces a BSON::Document when used with a block' do
+        result = enumerator.each(&:upcase)
+        expect(result).to be_a(described_class)
+        expect(result).to eq(described_class.new('KEY1' => 'value1', 'KEY2' => 'value2', 'KEY3' => 'value3'))
+      end
+    end
+  end
+
+  describe '#transform_keys!' do
+    let(:result) do
+      document.transform_keys!(&:upcase)
+    end
+
+    it 'returns self' do
+      expect(result).to be(document)
+    end
+
+    it 'transforms all keys according to the block' do
+      result
+      expect(document.keys).to eq(%w[KEY1 KEY2 KEY3])
+    end
+
+    context 'with nested documents' do
+      let(:document) do
+        described_class.new('outer' => described_class.new('inner' => 'value'))
+      end
+
+      let(:result) do
+        document.transform_keys!(&:upcase)
+      end
+
+      it 'does not transform keys in nested documents' do
+        result
+        expect(document['OUTER'].keys).to eq([ 'inner' ])
+      end
+
+      it 'preserves nested BSON::Document' do
+        result
+        expect(document['OUTER']).to be_a(described_class)
+      end
+    end
+
+    context 'transforming to keys to String' do
+      let(:document) do
+        described_class.new('key' => :a, 1 => :b)
+      end
+
+      let(:action) do
+        document.transform_keys!(&:to_s)
+      end
+
+      it 'transforms keys to String' do
+        action
+        expect(document).to eq('key' => :a, '1' => :b)
+      end
+    end
+
+    context 'transforming to keys to Symbol' do
+      let(:document) do
+        described_class.new('key' => :a, 1 => :b)
+      end
+
+      let(:action) do
+        document.transform_keys! { |key| key.is_a?(String) ? key.to_sym : key }
+      end
+
+      it 'transforms keys to String' do
+        action
+        expect(document).to eq('key' => :a, 1 => :b)
+      end
+    end
+
+    context 'when block not given' do
+      let(:enumerator) do
+        document.transform_keys!
+      end
+
+      it 'returns an enumerator' do
+        expect(enumerator).to be_a(Enumerator)
+      end
+
+      it 'enumerates over all keys' do
+        expect(enumerator.to_a).to eq(%w[key1 key2 key3])
+
+        # Side effect of calling #to_a, same as behavior on Hash.
+        expect(document).to eq(nil => 'value3')
+      end
+
+      it 'modifies the original document when used with a block' do
+        result = document.transform_keys!.each(&:upcase)
+        expect(result).to be(document)
+        expect(document).to eq(described_class.new('KEY1' => 'value1', 'KEY2' => 'value2', 'KEY3' => 'value3'))
+      end
+    end
+  end
+
+  describe '#transform_values' do
+    let(:result) do
+      document.transform_values(&:upcase)
+    end
+
+    it 'returns a new BSON::Document' do
+      expect(result).to be_a(described_class)
+      expect(result).not_to be(document)
+    end
+
+    it 'transforms all values according to the block' do
+      expect(result).to eq({ 'key1' => 'VALUE1', 'key2' => 'VALUE2', 'key3' => 'VALUE3' })
+    end
+
+    it 'does not modify the original document' do
+      result
+      expect(document).to eq(described_class.new('key1' => 'value1', 'key2' => 'value2', 'key3' => 'value3'))
+    end
+
+    context 'with nested documents' do
+      let(:document) do
+        described_class.new('key1' => described_class.new('inner' => 'value'))
+      end
+
+      let(:result) do
+        document.transform_values { |value| value }
+      end
+
+      it 'preserves nested documents' do
+        original_nested = document['key1']
+        nested = result['key1']
+        expect(nested).to be_a(described_class)
+        expect(nested).to eq(original_nested)
+      end
+    end
+
+    context 'transforming nested documents' do
+      let(:document) do
+        described_class.new('key1' => described_class.new('inner' => 'value'))
+      end
+
+      let(:result) do
+        document.transform_values! { |value| value.is_a?(described_class) ? { foo: :bar, 1 => :a } : value }
+      end
+
+      it 'allows transforming nested documents' do
+        expect(result).to eq(described_class.new('key1' => { 'foo' => :bar, 1 => :a }))
+      end
+
+      it 'converts nested values to BSON::Document' do
+        nested = result['key1']
+        expect(nested).to be_a(described_class)
+        expect(nested.keys).to eq([ 'foo', 1 ])
+      end
+    end
+
+    context 'when block not given' do
+      let(:enumerator) do
+        document.transform_values
+      end
+
+      it 'returns an enumerator' do
+        expect(enumerator).to be_a(Enumerator)
+      end
+
+      it 'enumerates over all values' do
+        expect(enumerator.to_a).to eq(document.values)
+      end
+
+      it 'produces a BSON::Document when used with a block' do
+        result = enumerator.each(&:upcase)
+        expect(result).to be_a(described_class)
+        expect(result).to eq(described_class.new('key1' => 'VALUE1', 'key2' => 'VALUE2', 'key3' => 'VALUE3'))
+      end
+
+      context 'with nested documents' do
+        let(:document) do
+          described_class.new('key1' => 'value1', 'nested' => described_class.new('inner' => 'value'))
+        end
+
+        let(:nested_enumerator) do
+          document.transform_values
+        end
+
+        it 'properly handles nested documents when used with a block' do
+          result = nested_enumerator.each { |value| value.is_a?(described_class) ? value.dup : value }
+          expect(result).to be_a(described_class)
+          expect(result['nested']).to be_a(described_class)
+          expect(result['nested']).to eq(described_class.new('inner' => 'value'))
+        end
+      end
+
+      context 'enumerator for nested documents' do
+        let(:document) do
+          described_class.new(
+            'key1' => 'value1',
+            'nested' => described_class.new(
+              'inner1' => 'value2',
+              'inner2' => described_class.new('deep' => 'value3')
+            )
+          )
+        end
+
+        it 'preserves class of nested documents in transformations' do
+          # Using transform_values with an identity block should preserve all types
+          result = document.transform_values { |v| v }
+          expect(result['nested']).to be_a(described_class)
+          expect(result['nested']['inner2']).to be_a(described_class)
+        end
+
+        it 'allows transforming nested documents with enumerator' do
+          document.transform_values!.each { |v| v } # rubocop:disable Lint/Void
+          expect(document['nested']).to be_a(described_class)
+          expect(document['nested']['inner2']).to be_a(described_class)
+        end
+      end
+
+      context 'chaining enumerators' do
+        it 'allows chaining operations on the returned enumerator' do
+          result = document.transform_values.with_index do |value, i|
+            "#{value}-#{i}"
+          end
+
+          expect(result).to be_a(described_class)
+          expect(result).to eq(
+            described_class.new('key1' => 'value1-0', 'key2' => 'value2-1', 'key3' => 'value3-2')
+          )
+        end
+      end
+    end
+  end
+
+  describe '#transform_values!' do
+    let(:result) do
+      document.transform_values!(&:upcase)
+    end
+
+    it 'returns self' do
+      expect(result).to be(document)
+    end
+
+    it 'transforms all values according to the block' do
+      result
+      expect(document).to eq(described_class.new('key1' => 'VALUE1', 'key2' => 'VALUE2', 'key3' => 'VALUE3'))
+    end
+
+    context 'with nested documents' do
+      let(:document) do
+        described_class.new('key1' => described_class.new('inner' => 'value'))
+      end
+
+      let(:action) do
+        document.transform_values! { |value| value }
+      end
+
+      it 'preserves nested documents' do
+        original_nested = document['key1']
+        action
+        nested = document['key1']
+        expect(nested).to be_a(described_class)
+        expect(nested).to eq(original_nested)
+      end
+    end
+
+    context 'transforming nested documents' do
+      let(:document) do
+        described_class.new('key1' => described_class.new('inner' => 'value'))
+      end
+
+      let(:action) do
+        document.transform_values! { |value| value.is_a?(described_class) ? { foo: :bar, 1 => :a } : value }
+      end
+
+      it 'allows transforming nested documents' do
+        action
+        expect(document).to eq(described_class.new('key1' => { 'foo' => :bar, 1 => :a }))
+      end
+
+      it 'converts nested values to BSON::Document' do
+        action
+        nested = document['key1']
+        expect(nested).to be_a(described_class)
+        expect(nested.keys).to eq([ 'foo', 1 ])
+      end
+    end
+
+    context 'when block not given' do
+      let(:enumerator) do
+        document.dup.transform_values!
+      end
+
+      it 'returns an enumerator' do
+        expect(enumerator).to be_a(Enumerator)
+      end
+
+      it 'enumerates over all values' do
+        expect(enumerator.to_a).to eq(document.values)
+      end
+
+      it 'modifies the original document when used with a block' do
+        result = document.transform_values!.each(&:upcase)
+        expect(result).to be(document)
+        expect(document).to eq(described_class.new('key1' => 'VALUE1', 'key2' => 'VALUE2', 'key3' => 'VALUE3'))
+      end
+    end
+  end
+end
diff --git a/spec/bson/document_spec.rb b/spec/bson/document_spec.rb
index 59102b019..95254d411 100644
--- a/spec/bson/document_spec.rb
+++ b/spec/bson/document_spec.rb
@@ -185,61 +185,57 @@
     end
   end
 
-  if described_class.instance_methods.include?(:dig)
-    describe "#dig" do
-      let(:document) do
-        described_class.new("key1" => { :key2 => "value" })
-      end
+  describe "#dig" do
+    let(:document) do
+      described_class.new("key1" => { :key2 => "value" })
+    end
 
-      context "when provided string keys" do
+    context "when provided string keys" do
 
-        it "returns the value" do
-          expect(document.dig("key1", "key2")).to eq("value")
-        end
+      it "returns the value" do
+        expect(document.dig("key1", "key2")).to eq("value")
       end
+    end
 
-      context "when provided symbol keys" do
+    context "when provided symbol keys" do
 
-        it "returns the value" do
-          expect(document.dig(:key1, :key2)).to eq("value")
-        end
+      it "returns the value" do
+        expect(document.dig(:key1, :key2)).to eq("value")
       end
     end
   end
 
-  if described_class.instance_methods.include?(:slice)
-    describe "#slice" do
-      let(:document) do
-        described_class.new("key1" => "value1", key2: "value2")
-      end
+  describe "#slice" do
+    let(:document) do
+      described_class.new("key1" => "value1", key2: "value2")
+    end
 
-      context "when provided string keys" do
+    context "when provided string keys" do
 
-        it "is a BSON Document" do
-          expect(document.slice("key1")).to be_a(BSON::Document)
-        end
+      it "is a BSON Document" do
+        expect(document.slice("key1")).to be_a(BSON::Document)
+      end
 
-        it "returns the partial document" do
-          expect(document.slice("key1")).to contain_exactly(['key1', 'value1'])
-        end
+      it "returns the partial document" do
+        expect(document.slice("key1")).to contain_exactly(['key1', 'value1'])
       end
+    end
 
-      context "when provided symbol keys" do
+    context "when provided symbol keys" do
 
-        it "is a BSON Document" do
-          expect(document.slice(:key1)).to be_a(BSON::Document)
-        end
+      it "is a BSON Document" do
+        expect(document.slice(:key1)).to be_a(BSON::Document)
+      end
 
-        it "returns the partial document" do
-          expect(document.slice(:key1)).to contain_exactly(['key1', 'value1'])
-        end
+      it "returns the partial document" do
+        expect(document.slice(:key1)).to contain_exactly(['key1', 'value1'])
       end
+    end
 
-      context "when provided keys that do not exist in the document" do
+    context "when provided keys that do not exist in the document" do
 
-        it "returns only the keys that exist in the document" do
-          expect(document.slice(:key1, :key3)).to contain_exactly(['key1', 'value1'])
-        end
+      it "returns only the keys that exist in the document" do
+        expect(document.slice(:key1, :key3)).to contain_exactly(['key1', 'value1'])
       end
     end
   end
@@ -264,7 +260,6 @@
     end
   end
 
-
   describe "#delete" do
 
     shared_examples_for "a document with deletable pairs" do
diff --git a/spec/spec_helper.rb b/spec/spec_helper.rb
index 009443323..206c7990b 100644
--- a/spec/spec_helper.rb
+++ b/spec/spec_helper.rb
@@ -40,6 +40,7 @@
     # https://github.com/rails/rails/issues/43889, etc.
     require 'active_support'
   end
+  require "active_support/core_ext"
   require "active_support/time"
   require 'bson/active_support'
 end