Only include ActiveRecord matchers if AR is defined

Fixes cases where you may be using ActiveModel without ActiveRecord.

Also add a test for loading without ActiveRecord.

The Cucumber feature creates a Gemfile containing ActiveModel and
shoulda-matchers, and then asserts that both can be loaded without any
errors.

The ActiveModel version used will match that of the Rails version
specified in the Appraisal Gemfile; and if no such version can be
determined, the latest will be used.

Closes #480.

NEWS.md

@@ -3,6 +3,9 @@
 * Fix `ComparisonMatcher` so that `validate_numericality_of` comparison matchers
   work with large numbers (#483).
 
+* Fix so that ActiveRecord matchers aren't included when ActiveRecord
+  isn't defined (i.e. if you are using ActiveModel only).
+
 # 2.6.0
 
 * The boolean argument to `have_db_index`'s `unique` option is now optional, for

features/activemodel_integration.feature

@@ -0,0 +1,15 @@
+Feature: integration with ActiveModel
+
+  Scenario: create a new project using matchers
+    When I generate a new ActiveModel application
+    And I configure the application to use "shoulda-matchers" from this project
+    And I write to "load_dependencies.rb" with:
+      """
+      require 'active_model'
+      require 'shoulda-matchers'
+
+      puts ActiveModel::VERSION::STRING
+      puts "Loaded all dependencies without errors"
+      """
+    When I successfully run `bundle exec ruby load_dependencies.rb`
+    Then the output should contain "Loaded all dependencies without errors"

features/step_definitions/activemodel_steps.rb

@@ -0,0 +1,21 @@
+When 'I generate a new ActiveModel application' do
+  steps %{
+    When I run `mkdir #{APP_NAME}`
+    And I cd to "#{APP_NAME}"
+    And I run `bundle init`
+  }
+
+  # Figure out the ActiveModel version to use by reusing the Rails version from
+  # the Appraise gemfile.
+  if match = File.read(ENV['BUNDLE_GEMFILE']).match(/^gem "rails", "(.*)"/)
+    append_to_gemfile %(gem 'activemodel', '#{ match[1] }')
+  else
+    puts "Couldn't determine which ActiveModel version to load; using latest"
+    append_to_gemfile %(gem 'activemodel')
+  end
+
+  steps %{
+    And I set the "BUNDLE_GEMFILE" environment variable to "Gemfile"
+    And I install gems
+  }
+end

lib/shoulda/matchers/integrations/test_unit.rb

@@ -21,12 +21,14 @@ end
 
 if defined?(ActiveSupport::TestCase)
   ActiveSupport::TestCase.class_eval do
-    include Shoulda::Matchers::ActiveRecord
-    extend Shoulda::Matchers::ActiveRecord
-  end
+    if defined?(Shoulda::Matchers::ActiveRecord)
+      include Shoulda::Matchers::ActiveRecord
+      extend Shoulda::Matchers::ActiveRecord
+    end
 
-  ActiveSupport::TestCase.class_eval do
-    include Shoulda::Matchers::ActiveModel
-    extend Shoulda::Matchers::ActiveModel
+    if defined?(Shoulda::Matchers::ActiveModel)
+      include Shoulda::Matchers::ActiveModel
+      extend Shoulda::Matchers::ActiveModel
+    end
   end
 end