diff --git a/exercises/grains/.meta/.version b/exercises/grains/.meta/.version
new file mode 100644
index 0000000000..56a6051ca2
--- /dev/null
+++ b/exercises/grains/.meta/.version
@@ -0,0 +1 @@
+1
\ No newline at end of file
diff --git a/exercises/grains/example.rb b/exercises/grains/example.rb
index 5afad3b8db..0ebb75cc42 100644
--- a/exercises/grains/example.rb
+++ b/exercises/grains/example.rb
@@ -1,9 +1,14 @@
+module BookKeeping
+  VERSION = 1
+end
+
 module Grains
   def self.square(number)
+    fail ArgumentError if number <= 0 || number > 64
     2**(number - 1)
   end
 
   def self.total
-    square(65) - 1
+    2**64 - 1
   end
 end
diff --git a/exercises/grains/example.tt b/exercises/grains/example.tt
new file mode 100644
index 0000000000..6aa03653e2
--- /dev/null
+++ b/exercises/grains/example.tt
@@ -0,0 +1,17 @@
+require 'minitest/autorun'
+require_relative 'grains'
+
+# Test data version: <%= sha1 %>
+class GrainsTest < Minitest::Test<% test_cases.each do |test_case| %>
+  def <%= test_case.test_name %>
+    <%= test_case.skipped %>
+    <%= test_case.workload %>
+  end
+<% end %>
+
+<%= IO.read(XRUBY_LIB + '/bookkeeping.md') %>
+  def test_bookkeeping
+    skip
+    assert_equal <%= version.next %>, BookKeeping::VERSION
+  end
+end
diff --git a/exercises/grains/grains_test.rb b/exercises/grains/grains_test.rb
index 9f4dcc7933..db99758d62 100755
--- a/exercises/grains/grains_test.rb
+++ b/exercises/grains/grains_test.rb
@@ -1,45 +1,81 @@
-#!/usr/bin/env ruby
-gem 'minitest', '>= 5.0.0'
 require 'minitest/autorun'
 require_relative 'grains'
 
+# Test data version: aa12f2e
 class GrainsTest < Minitest::Test
-  def test_square_1
+  def test_1
+    # skip
     assert_equal 1, Grains.square(1)
   end
 
-  def test_square_2
+  def test_2
     skip
     assert_equal 2, Grains.square(2)
   end
 
-  def test_square_3
+  def test_3
     skip
     assert_equal 4, Grains.square(3)
   end
 
-  def test_square_4
+  def test_4
     skip
     assert_equal 8, Grains.square(4)
   end
 
-  def test_square_16
+  def test_16
     skip
     assert_equal 32_768, Grains.square(16)
   end
 
-  def test_square_32
+  def test_32
     skip
     assert_equal 2_147_483_648, Grains.square(32)
   end
 
-  def test_square_64
+  def test_64
     skip
     assert_equal 9_223_372_036_854_775_808, Grains.square(64)
   end
 
-  def test_total_grains
+  def test_square_0_raises_an_exception
+    skip
+    assert_raises(ArgumentError) { Grains.square(0) }
+  end
+
+  def test_negative_square_raises_an_exception
+    skip
+    assert_raises(ArgumentError) { Grains.square(-1) }
+  end
+
+  def test_square_greater_than_64_raises_an_exception
+    skip
+    assert_raises(ArgumentError) { Grains.square(65) }
+  end
+
+  def test_returns_the_total_number_of_grains_on_the_board
     skip
     assert_equal 18_446_744_073_709_551_615, Grains.total
   end
+
+  # Problems in exercism evolve over time, as we find better ways to ask
+  # questions.
+  # The version number refers to the version of the problem you solved,
+  # not your solution.
+  #
+  # Define a constant named VERSION inside of the top level BookKeeping
+  # module, which may be placed near the end of your file.
+  #
+  # In your file, it will look like this:
+  #
+  # module BookKeeping
+  #   VERSION = 1 # Where the version number matches the one in the test.
+  # end
+  #
+  # If you are curious, read more about constants on RubyDoc:
+  # http://ruby-doc.org/docs/ruby-doc-bundle/UsersGuide/rg/constants.html
+  def test_bookkeeping
+    skip
+    assert_equal 1, BookKeeping::VERSION
+  end
 end
diff --git a/lib/grains_cases.rb b/lib/grains_cases.rb
new file mode 100644
index 0000000000..e7419bbb72
--- /dev/null
+++ b/lib/grains_cases.rb
@@ -0,0 +1,51 @@
+class GrainsCase < OpenStruct
+  def test_name
+    'test_%s' % description.downcase.tr_s(' ', '_')
+  end
+
+  def workload
+    fail NotImplementedError
+  end
+
+  def skipped
+    index.zero? ? '# skip' : 'skip'
+  end
+
+  private
+
+  def underscore_format(number)
+    number.to_s.reverse.gsub(/...(?=.)/,'\&_').reverse
+  end
+end
+
+class GrainsCase::SquareMethod < GrainsCase
+  def workload
+    return error_assertion if expected < 0
+
+    "assert_equal #{underscore_format(expected)}, Grains.square(#{input})"
+  end
+
+  private
+
+  def error_assertion
+    "assert_raises(ArgumentError) { Grains.square(#{input}) }"
+  end
+end
+
+class GrainsCase::TotalMethod < GrainsCase
+  def workload
+    "assert_equal #{underscore_format(expected)}, Grains.total"
+  end
+end
+
+GrainsCases = proc do |data|
+  data = JSON.parse(data)
+
+  cases = data['square']['cases'].map.with_index do |row, i|
+    GrainsCase::SquareMethod.new(row.merge('index' => i))
+  end
+
+  cases << GrainsCase::TotalMethod.new(
+    data['total'].merge('index' => cases.size)
+  )
+end
diff --git a/test/grains_cases_test.rb b/test/grains_cases_test.rb
new file mode 100644
index 0000000000..cee8b7fdc7
--- /dev/null
+++ b/test/grains_cases_test.rb
@@ -0,0 +1,102 @@
+require_relative 'test_helper'
+
+class GrainsTest < Minitest::Test
+  def test_test_name
+    test_case = GrainsCase.new(description: 'description')
+
+    assert_equal 'test_description', test_case.test_name
+  end
+
+  def test_test_name_when_description_has_spaces
+    test_case = GrainsCase.new(description: 'description with spaces')
+
+    assert_equal 'test_description_with_spaces', test_case.test_name
+  end
+
+  def test_workload_is_not_implemented
+    assert_raises(NotImplementedError) { GrainsCase.new.workload }
+  end
+
+  def test_skipped_with_zero_index
+    assert_equal '# skip', GrainsCase.new(index: 0).skipped
+  end
+
+  def test_skipped_with_non_zero_index
+    assert_equal 'skip', GrainsCase.new(index: 1).skipped
+  end
+end
+
+class SquareMethodTest < Minitest::Test
+  def test_workload_when_expected_is_negative
+    test_case = GrainsCase::SquareMethod.new(expected: -1, input: 10)
+
+    assert_equal 'assert_raises(ArgumentError) { Grains.square(10) }',
+                 test_case.workload
+  end
+
+  def test_workload_when_expected_is_positive
+    test_case = GrainsCase::SquareMethod.new(expected: 1, input: 10)
+
+    assert_equal 'assert_equal 1, Grains.square(10)', test_case.workload
+  end
+
+  def test_workload_with_large_expected_number
+    test_case = GrainsCase::SquareMethod.new(expected: 10000, input: 10)
+
+    assert_equal 'assert_equal 10_000, Grains.square(10)', test_case.workload
+  end
+end
+
+class TotalMethodTest < Minitest::Test
+  def test_workload
+    test_case = GrainsCase::TotalMethod.new(expected: 1)
+
+    assert_equal 'assert_equal 1, Grains.total', test_case.workload
+  end
+
+  def test_workload_with_large_expected_number
+    test_case = GrainsCase::TotalMethod.new(expected: 10000)
+
+    assert_equal 'assert_equal 10_000, Grains.total', test_case.workload
+  end
+end
+
+class GrainsCasesTest < Minitest::Test
+  def test_handling_of_json
+    json = {
+      square: {
+        cases: [
+          {},
+          {},
+        ],
+      },
+      total: {
+      }
+    }.to_json
+
+    cases = GrainsCases.call(json)
+
+    assert_instance_of GrainsCase::SquareMethod, cases[0]
+    assert_instance_of GrainsCase::SquareMethod, cases[1]
+    assert_instance_of GrainsCase::TotalMethod, cases[2]
+  end
+
+  def test_continuous_index
+    json = {
+      square: {
+        cases: [
+          {},
+          {},
+        ],
+      },
+      total: {
+      }
+    }.to_json
+
+    cases = GrainsCases.call(json)
+
+    assert_equal 0, cases[0].index
+    assert_equal 1, cases[1].index
+    assert_equal 2, cases[2].index
+  end
+end