use rspec-rails logic for test unit assertions

Author: JonRowe

Gemfile

@@ -20,7 +20,7 @@ group :documentation do
   gem 'github-markup', '1.0.0'
 end
 
-case version = ENV.fetch('RAILS_VERSION', '4.0.2')
+case version = ENV.fetch('RAILS_VERSION', '4.2.4')
 when /\Amaster\z/, /stable\z/
   gem "activerecord", :github => "rails/rails", :branch => version
   gem "activemodel", :github => "rails/rails", :branch => version
@@ -31,4 +31,6 @@ else
   gem "activesupport", version
 end
 
+gem "test-unit", '~> 3' if version >= '3.2.22' && version < '4.0.0'
+
 gem "i18n", '< 0.7.0' if RUBY_VERSION < '1.9.3'

spec/rspec/active_model/mocks/mock_model_spec.rb

@@ -414,8 +414,45 @@
       include Minitest::Assertions
       include MinitestAssertion
     rescue LoadError
-      require 'test/unit/assertions'
-      include Test::Unit::Assertions
+      if RUBY_VERSION >= '2.2.0'
+        # Minitest / TestUnit has been removed from ruby core. However, we are
+        # on an old Rails version and must load the appropriate gem
+        version = ENV.fetch('RAILS_VERSION', '4.2.4')
+        if version >= '4.0.0'
+          # ActiveSupport 4.0.x has the minitest '~> 4.2' gem as a dependency
+          # This gem has no `lib/minitest.rb` file.
+          gem 'minitest' if defined?(Kernel.gem)
+          require 'minitest/unit'
+          Assertions = MiniTest::Assertions
+        elsif version >= '3.2.22'
+          begin
+            # Test::Unit "helpfully" sets up autoload for its `AutoRunner`.
+            # While we do not reference it directly, when we load the `TestCase`
+            # classes from AS (ActiveSupport), AS kindly references `AutoRunner`
+            # for everyone.
+            #
+            # To handle this we need to pre-emptively load 'test/unit' and make
+            # sure the version installed has `AutoRunner` (the 3.x line does to
+            # date). If so, we turn the auto runner off.
+            require 'test/unit'
+            require 'test/unit/assertions'
+          rescue LoadError => e
+            raise LoadError, <<-ERR.squeeze, e.backtrace
+              Ruby 2.2+ has removed test/unit from the core library. Rails
+              requires this as a dependency. Please add test-unit gem to your
+              Gemfile: `gem 'test-unit', '~> 3.0'` (#{e.message})"
+            ERR
+          end
+          Assertions = Test::Unit::Assertions
+        else
+          raise LoadError, <<-ERR.squeeze
+            Ruby 2.2+ doesn't support this version of Rails #{version}
+          ERR
+        end
+      else
+        require 'test/unit/assertions'
+        include Test::Unit::Assertions
+      end
     end
 
     require 'active_model/lint'