diff --git a/app/models/app.rb b/app/models/app.rb
index 4f8d4325..afae7ba5 100644
--- a/app/models/app.rb
+++ b/app/models/app.rb
@@ -2,9 +2,14 @@
 
 # App is utility module specific to this Rails Application and its environment.
 module App
-  def self.exclude_test_difficulty_level?
-    @exclude_test_difficulty_level ||=
-      !debug? && Game.for_difficulty_level_test.none?
+  # :reek:NilCheck
+  def self.include_test_difficulty_level?
+    if @include_test_difficulty_level.nil?
+      @include_test_difficulty_level =
+        debug? || Game.for_difficulty_level_test.any?
+    else
+      @include_test_difficulty_level
+    end
   end
 
   def self.debug? = Rails.configuration.debug
diff --git a/app/models/difficulty_level.rb b/app/models/difficulty_level.rb
index 895057d8..3f3c15c0 100644
--- a/app/models/difficulty_level.rb
+++ b/app/models/difficulty_level.rb
@@ -10,14 +10,18 @@ class DifficultyLevel
   # DifficultyLevel processing.
   Error = Class.new(StandardError)
 
-  SETTINGS_MAP = {
-    TEST = "Test" => { columns: 3, rows: 3, mines: 1 },
-    "Beginner" => { columns: 9, rows: 9, mines: 10 },
-    "Intermediate" => { columns: 16, rows: 16, mines: 40 },
-    "Expert" => { columns: 30, rows: 16, mines: 99 },
-  }.tap { |hash|
-    hash.except!(TEST) if App.exclude_test_difficulty_level?
-  }.freeze
+  TEST = "Test"
+
+  def self.settings_map
+    @settings_map ||= {
+      TEST => { columns: 3, rows: 3, mines: 1 },
+      "Beginner" => { columns: 9, rows: 9, mines: 10 },
+      "Intermediate" => { columns: 16, rows: 16, mines: 40 },
+      "Expert" => { columns: 30, rows: 16, mines: 99 },
+    }.tap { |hash|
+      hash.except!(TEST) unless App.include_test_difficulty_level?
+    }.freeze
+  end
 
   attr_reader :name
 
@@ -26,7 +30,7 @@ def self.all
   end
 
   def self.names
-    SETTINGS_MAP.keys
+    settings_map.keys
   end
 
   def self.build_random
@@ -67,7 +71,7 @@ def rows = settings.fetch(:rows)
   def mines = settings.fetch(:mines)
 
   def settings
-    SETTINGS_MAP.fetch(name)
+    self.class.settings_map.fetch(name)
   end
 
   private
diff --git a/test/models/app_test.rb b/test/models/app_test.rb
new file mode 100644
index 00000000..d34b83e8
--- /dev/null
+++ b/test/models/app_test.rb
@@ -0,0 +1,113 @@
+# frozen_string_literal: true
+
+require "test_helper"
+
+class AppTest < ActiveSupport::TestCase
+  describe "App" do
+    let(:unit_class) { App }
+
+    subject { unit_class }
+
+    describe ".include_test_difficulty_level?" do
+      before do
+        App.instance_variable_set(:@include_test_difficulty_level, nil)
+      end
+
+      after do
+        App.instance_variable_set(:@include_test_difficulty_level, nil)
+      end
+
+      context "GIVEN App.debug? = true" do
+        before do
+          MuchStub.(unit_class, :debug?) { true }
+        end
+
+        context "WHETHER OR NOT any 'Test' Games exist" do
+          before do
+            MuchStub.tap(Game, :for_difficulty_level_test) { |arel|
+              MuchStub.(arel, :any?) { [true, false].sample }
+            }
+          end
+
+          it "returns true" do
+            _(subject.include_test_difficulty_level?).must_equal(true)
+          end
+        end
+      end
+
+      context "GIVEN App.debug? = false" do
+        before do
+          MuchStub.(unit_class, :debug?) { false }
+        end
+
+        context "GIVEN 'Test' Games do exist" do
+          before do
+            MuchStub.tap(Game, :for_difficulty_level_test) { |arel|
+              MuchStub.(arel, :any?) { true }
+            }
+          end
+
+          it "returns true" do
+            _(subject.include_test_difficulty_level?).must_equal(true)
+          end
+        end
+
+        context "GIVEN no 'Test' Games exist" do
+          before do
+            MuchStub.tap(Game, :for_difficulty_level_test) { |arel|
+              MuchStub.(arel, :any?) { false }
+            }
+          end
+
+          it "returns false" do
+            _(subject.include_test_difficulty_level?).must_equal(false)
+          end
+        end
+
+        context "GIVEN multiple calls" do
+          before do
+            @any_called_count = 0
+            MuchStub.tap(Game, :for_difficulty_level_test) { |arel|
+              MuchStub.(arel, :any?) {
+                @any_called_count += 1
+                false
+              }
+            }
+          end
+
+          it "uses a memoized result" do
+            subject.include_test_difficulty_level?
+            subject.include_test_difficulty_level?
+            _(@any_called_count).must_equal(1)
+          end
+        end
+      end
+    end
+
+    describe ".debug?" do
+      context "GIVEN Rails.configuration.debug = true" do
+        before do
+          MuchStub.tap(Rails, :configuration) { |config|
+            MuchStub.(config, :debug) { true }
+          }
+        end
+
+        it "returns true" do
+          _(subject.debug?).must_equal(true)
+        end
+      end
+
+      context "GIVEN Rails.configuration.debug = false" do
+        before do
+          MuchStub.tap(Rails, :configuration) { |config|
+            MuchStub.(config, :debug) { false }
+          }
+        end
+
+        it "returns false" do
+          _(subject.debug?).must_equal(false)
+        end
+      end
+    end
+  end
+end
diff --git a/test/models/random_difficulty_level_test.rb b/test/models/random_difficulty_level_test.rb
index c0b6b777..3829c282 100644
--- a/test/models/random_difficulty_level_test.rb
+++ b/test/models/random_difficulty_level_test.rb
@@ -10,9 +10,10 @@ class RandomDifficultyLevelTest < ActiveSupport::TestCase
       subject { unit_class }
 
       describe "#initialize" do
-        it "returns the expected instance" do
+        it "returns a frozen RandomDifficultyLevel instance" do
           result = subject.new
           _(result).must_be_instance_of(unit_class)
+          _(result.frozen?).must_equal(true)
         end
       end
     end