1 files changed, 61 insertions, 0 deletions
diff --git a/activesupport/lib/active_support/testing/assertions.rb b/activesupport/lib/active_support/testing/assertions.rb
new file mode 100644
index 0000000000..7665d9217e
--- /dev/null
+++ b/activesupport/lib/active_support/testing/assertions.rb
@@ -0,0 +1,61 @@
+module ActiveSupport
+  module Testing
+    module Assertions
+      # Test numeric difference between the return value of an expression as a result of what is evaluated
+      # in the yielded block.
+      #
+      #   assert_difference 'Article.count' do
+      #     post :create, :article => {...}
+      #   end
+      #
+      # An arbitrary expression is passed in and evaluated.
+      #
+      #   assert_difference 'assigns(:article).comments(:reload).size' do
+      #     post :create, :comment => {...}
+      #   end
+      #
+      # An arbitrary positive or negative difference can be specified. The default is +1.
+      #
+      #   assert_difference 'Article.count', -1 do
+      #     post :delete, :id => ...
+      #   end
+      #
+      # An array of expressions can also be passed in and evaluated.
+      #
+      #   assert_difference [ 'Article.count', 'Post.count' ], +2 do
+      #     post :create, :article => {...}
+      #   end
+      #
+      # A error message can be specified.
+      #
+      #   assert_difference 'Article.count', -1, "An Article should be destroyed" do
+      #     post :delete, :id => ...
+      #   end
+      def assert_difference(expressions, difference = 1, message = nil, &block)
+        expression_evaluations = Array(expressions).collect{ |expression| lambda { eval(expression, block.send!(:binding)) } }
+
+        original_values = expression_evaluations.inject([]) { |memo, expression| memo << expression.call }
+        yield
+        expression_evaluations.each_with_index do |expression, i|
+          assert_equal original_values[i] + difference, expression.call, message
+        end
+      end
+
+      # Assertion that the numeric result of evaluating an expression is not changed before and after
+      # invoking the passed in block.
+      #
+      #   assert_no_difference 'Article.count' do
+      #     post :create, :article => invalid_attributes
+      #   end
+      #
+      # A error message can be specified.
+      #
+      #   assert_no_difference 'Article.count', "An Article should not be destroyed" do
+      #     post :create, :article => invalid_attributes
+      #   end
+      def assert_no_difference(expressions, message = nil, &block)
+        assert_difference expressions, 0, message, &block
+      end
+    end
+  end
+end