diff --git a/Gemfile b/Gemfile
new file mode 100644
index 0000000..d34982f
--- /dev/null
+++ b/Gemfile
@@ -0,0 +1,4 @@
+# A sample Gemfile
+source "https://rubygems.org"
+
+gem "mocha"
diff --git a/Gemfile.lock b/Gemfile.lock
new file mode 100644
index 0000000..2ef099e
--- /dev/null
+++ b/Gemfile.lock
@@ -0,0 +1,12 @@
+GEM
+  remote: https://rubygems.org/
+  specs:
+    metaclass (0.0.4)
+    mocha (1.0.0)
+      metaclass (~> 0.0.1)
+
+PLATFORMS
+  ruby
+
+DEPENDENCIES
+  mocha
diff --git a/lib/sudoku_validator.rb b/lib/sudoku_validator.rb
new file mode 100644
index 0000000..7a3305a
--- /dev/null
+++ b/lib/sudoku_validator.rb
@@ -0,0 +1,93 @@
+class SudokuFileParser
+  attr_reader :grid
+
+  def initialize(filename)
+    contents = IO.read(filename)
+    stripped = strip_unnecessary(contents)
+    @grid = gridify(stripped)
+  end
+
+  private
+
+  def strip_unnecessary(contents)
+    contents.gsub(/[^\d\.]/, '')
+  end
+
+  def gridify(stripped)
+    stripped.chars.each_slice(9).to_a
+  end
+end
+
+
+class RowValidator
+  def initialize(grid)
+    @stripped_grid = strip_dots(grid)
+  end
+
+  def valid?
+    @stripped_grid.all? { |row| row.uniq.size == row.size }
+  end
+
+  private
+
+  def strip_dots(grid)
+    grid.map do |row|
+      row.reject { |e| e == '.' }
+    end
+  end
+end
+
+
+class ColumnValidator
+  def initialize(grid)
+    @validator = RowValidator.new(grid.transpose)
+  end
+
+  def valid?
+    @validator.valid?
+  end
+end
+
+
+class SubgridValidator
+  def initialize(grid)
+    modified_grid = subgrids_to_rows(grid)
+    @validator = RowValidator.new(modified_grid)
+  end
+
+  def valid?
+    @validator.valid?
+  end
+
+  private
+
+  def subgrids_to_rows(grid)
+    grid.each_slice(3).each_with_object([]) do |rows, new_grid|
+      new_grid.push(*row_of_subgrids(rows))
+    end
+  end
+
+  def row_of_subgrids(rows)
+    rows.flatten
+      .each_slice(3)                        # in triples
+      .group_by.with_index { |_, i| i % 3 } # group every third
+      .map { |i, e| e.flatten }             # form a row from subgrid elements
+  end
+end
+
+
+class SudokuValidator
+  def initialize(filename)
+    @grid = SudokuFileParser.new(filename).grid
+    @complete = !@grid.flatten.any? { |e| e == '.' }
+  end
+
+  def valid?
+    validators = [RowValidator, ColumnValidator, SubgridValidator]
+    validators.all? { |v| v.new(@grid).valid? }
+  end
+
+  def complete?
+    @complete
+  end
+end
diff --git a/sudoku-validator b/sudoku-validator
new file mode 100755
index 0000000..df1916c
--- /dev/null
+++ b/sudoku-validator
@@ -0,0 +1,12 @@
+#!/usr/bin/env ruby
+
+require_relative 'lib/sudoku_validator'
+
+app = SudokuValidator.new(ARGV.first)
+
+if app.valid?
+  ending = app.complete? ? '.' : ', but incomplete.'
+  puts "This sudoku is valid#{ending}"
+else
+  puts 'This sudoku is invalid.'
+end
diff --git a/invalid_complete.sudoku b/test/invalid_complete.sudoku
similarity index 100%
rename from invalid_complete.sudoku
rename to test/invalid_complete.sudoku
diff --git a/invalid_incomplete.sudoku b/test/invalid_incomplete.sudoku
similarity index 100%
rename from invalid_incomplete.sudoku
rename to test/invalid_incomplete.sudoku
diff --git a/test/sudoku_validator_test.rb b/test/sudoku_validator_test.rb
new file mode 100644
index 0000000..a4b33df
--- /dev/null
+++ b/test/sudoku_validator_test.rb
@@ -0,0 +1,130 @@
+require 'minitest/autorun'
+require 'minitest/pride'
+require 'mocha/mini_test'
+
+require_relative '../lib/sudoku_validator'
+
+class SudokuFileParserTest < MiniTest::Unit::TestCase
+  def test_reads_file_into_9x9_2d_array
+    parser = SudokuFileParser.new('test/valid_complete.sudoku')
+
+    assert_equal(9, parser.grid.size)
+    parser.grid.each { |row| assert_equal(9, row.size) }
+  end
+
+  def test_parses_as_strings
+    expected = 
+      [%w{8 5 . . . 2 4 . .},
+       %w{7 2 . . . . . . 9},
+       %w{. . 4 . . . . . .},
+       %w{. . . 1 . 7 . . 2},
+       %w{3 . 5 . . . 9 . .},
+       %w{. 4 . . . . . . .},
+       %w{. . . . 8 . . 7 .},
+       %w{. 1 7 . . . . . .},
+       %w{. . . . 3 6 . 4 .}]
+
+    parser = SudokuFileParser.new('test/valid_incomplete.sudoku')
+    assert_equal(expected, parser.grid)
+  end
+end
+
+class RowValidatorTest < MiniTest::Unit::TestCase
+  def test_valid_when_unique_in_row
+    grid = [%w{1 2 3}, %w{3 2 1}]
+
+    validator = RowValidator.new(grid)
+
+    assert(validator.valid?)
+  end
+
+  def test_invalid_when_duplicates_in_row
+    grid = [%w{1 2 3}, %w{3 2 3}]
+
+    validator = RowValidator.new(grid)
+
+    refute(validator.valid?)
+  end
+
+  def test_ignore_dots
+    assert(RowValidator.new([['.', '.'], ['.', '.']]).valid?)
+    assert(RowValidator.new([['.', '.'], ['1', '.']]).valid?)
+    refute(RowValidator.new([['.', '.', '2'], ['1', '.', '1']]).valid?)
+  end
+end
+
+class ColumnValidatorTest < MiniTest::Unit::TestCase
+  def test_is_implemented_in_terms_of_row_validator_for_transposed_grid
+    grid =[%w{1 2 3}, %w{4 5 6}]
+    row_validator = mock()
+    row_validator.expects(:valid?).returns(true)
+    RowValidator
+      .expects(:new)
+      .with([%w{1 4}, %w{2 5}, %w{3 6}])
+      .returns(row_validator)
+
+    ColumnValidator.new(grid).valid?
+  end
+end
+
+class SubgridValidatorTest < MiniTest::Unit::TestCase
+  def test_is_implemented_in_terms_of_row_validator_for_modified_grid
+    grid = 
+      [%w{8 5 . . . 2 4 . .},
+       %w{7 2 . . . . . . 9},
+       %w{. . 4 . . . . . .},
+       %w{. . . 1 . 7 . . 2},
+       %w{3 . 5 . . . 9 . .},
+       %w{. 4 . . . . . . .},
+       %w{. . . . 8 . . 7 .},
+       %w{. 1 7 . . . . . .},
+       %w{. . . . 3 6 . 4 .}]
+
+    modified_grid = 
+      [%w{8 5 . 7 2 . . . 4},
+       %w{. . 2 . . . . . .},
+       %w{4 . . . . 9 . . .},
+       %w{. . . 3 . 5 . 4 .},
+       %w{1 . 7 . . . . . .},
+       %w{. . 2 9 . . . . .},
+       %w{. . . . 1 7 . . .},
+       %w{. 8 . . . . . 3 6},
+       %w{. 7 . . . . . 4 .}]
+
+    row_validator = mock()
+    row_validator.expects(:valid?).returns(true)
+    RowValidator
+      .expects(:new)
+      .with(modified_grid)
+      .returns(row_validator)
+
+    SubgridValidator.new(grid).valid?
+  end
+end
+
+class SudokuValidatorTest < MiniTest::Unit::TestCase
+  def test_valid_complete
+    app = SudokuValidator.new('test/valid_complete.sudoku')
+    assert(app.valid?)
+    assert(app.complete?)
+  end
+
+  def test_valid_incomplete
+    app = SudokuValidator.new('test/valid_incomplete.sudoku')
+    assert(app.valid?)
+    refute(app.complete?)
+  end
+
+  def test_invalid_complete
+    app = SudokuValidator.new('test/invalid_complete.sudoku')
+    refute(app.valid?)
+    assert(app.complete?)
+  end
+
+  def test_invalid_incomplete
+    app = SudokuValidator.new('test/invalid_incomplete.sudoku')
+    refute(app.valid?)
+    refute(app.complete?)
+  end
+end
+
diff --git a/valid_complete.sudoku b/test/valid_complete.sudoku
similarity index 100%
rename from valid_complete.sudoku
rename to test/valid_complete.sudoku
diff --git a/valid_incomplete.sudoku b/test/valid_incomplete.sudoku
similarity index 100%
rename from valid_incomplete.sudoku
rename to test/valid_incomplete.sudoku