2 files changed, 31 insertions, 0 deletions
diff --git a/activesupport/lib/active_support/core_ext/test.rb b/activesupport/lib/active_support/core_ext/test.rb
new file mode 100644
index 0000000000..193599b8dc
--- /dev/null
+++ b/activesupport/lib/active_support/core_ext/test.rb
@@ -0,0 +1,2 @@
+require File.dirname(__FILE__) + '/test/difference'
+
diff --git a/activesupport/lib/active_support/core_ext/test/difference.rb b/activesupport/lib/active_support/core_ext/test/difference.rb
new file mode 100644
index 0000000000..1f85f0f4b7
--- /dev/null
+++ b/activesupport/lib/active_support/core_ext/test/difference.rb
@@ -0,0 +1,29 @@
+
+module Test #:nodoc:
+  module Unit #:nodoc:
+    class TestCase #:nodoc:
+      
+      # Test difference between the return value of method on object for duration of the block
+      def assert_difference(objects, method = nil, difference = 1)
+        objects = [objects].flatten
+        initial_values = objects.inject([]) { |sum,obj| sum << obj.send(method) }
+        yield
+        if difference.nil?
+          objects.each_with_index { |obj,i|
+            assert_not_equal initial_values[i], obj.send(method), "#{obj}##{method}"
+          }
+        else
+          objects.each_with_index { |obj,i|
+            assert_equal initial_values[i] + difference, obj.send(method), "#{obj}##{method}"
+          }
+        end
+      end
+
+      # Test absence of difference between the return value of method on object for duration of the block
+      def assert_no_difference(objects, method = nil, &block)
+        assert_difference objects, method, 0, &block
+      end
+
+    end
+  end
+end