Simplify API of assert_difference by passing in an expression that is evaluated before and after the passed in block. See documenation for examples of new API. [Marcel Molina Jr.]

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@6693 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

3 files changed, 64 insertions, 36 deletions

diff --git a/activesupport/CHANGELOG b/activesupport/CHANGELOG
index 28ff1136e2..1a1cb9c275 100644
--- a/activesupport/CHANGELOG
+++ b/activesupport/CHANGELOG
@@ -1,5 +1,7 @@
 *SVN*
 
+* Simplify API of assert_difference by passing in an expression that is evaluated before and after the passed in block. See documenation for examples of new API. [Marcel Molina Jr.]
+
 * Added assert_difference and assert_no_difference to test/unit assertions [Tobias Luetke]
 
 * Removed breakpointer and Binding.of_caller in favor of relying on ruby-debug by Kent Sibilev since the breakpointer has been broken since Ruby 1.8.4 and will not be coming back [DHH]
diff --git a/activesupport/lib/active_support/core_ext/test/difference.rb b/activesupport/lib/active_support/core_ext/test/difference.rb
index 1f85f0f4b7..65dae3469b 100644
--- a/activesupport/lib/active_support/core_ext/test/difference.rb
+++ b/activesupport/lib/active_support/core_ext/test/difference.rb
@@ -1,29 +1,40 @@
-
 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) }
+    class TestCase #:nodoc:      
+      # Test numeric difference between the return value of an expression as a result of what is evaluated
+      # in the yielded block.
+      #
+      #   assert_difference 'Post.count' do
+      #     post :create, :post => {...}
+      #   end
+      #
+      # An arbitrary expression is passed in an evaluated.
+      #
+      #   assert_difference 'assigns(:post).comments(:reload).size' do
+      #     post :create, :comment => {...}
+      #   end
+      #
+      # An arbitrary positive or negative difference can be specified. The default is 1.
+      #
+      #   assert_difference 'Post.count', -1 do
+      #     post :delete, :id => ...
+      #   end
+      def assert_difference(expression, difference = 1, &block)
+        expression_evaluation = lambda { eval(expression) }
+        original_value        = expression_evaluation.call
         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
+        assert_equal original_value + difference, expression_evaluation.call
       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
+      # Assertion that the numeric result of evaluating an expression is not changed before and after
+      # invoking the passed in block.
+      #
+      #   assert_no_difference 'Post.count' do
+      #     post :create, :post => invalid_attributes
+      #   end
+      def assert_no_difference(expression, &block)
+        assert_difference expression, 0, &block
       end
-
     end
   end
 end
diff --git a/activesupport/test/test_test.rb b/activesupport/test/test_test.rb
index 63a44e9379..d8a02b5497 100644
--- a/activesupport/test/test_test.rb
+++ b/activesupport/test/test_test.rb
@@ -3,32 +3,47 @@ require File.dirname(__FILE__) + '/abstract_unit'
 class AssertDifferenceTest < Test::Unit::TestCase
   
   def setup
-    @object = Class.new { attr_accessor :num }.new    
+    @object = Class.new do
+      attr_accessor :num 
+      def increment
+        self.num += 1
+      end
+
+      def decrement
+        self.num -= 1
+      end
+    end.new    
+    @object.num = 0
   end
   
   def test_assert_no_difference
-    @object.num = 0
-    
-    assert_no_difference @object, :num do
+    assert_no_difference '@object.num' do
       # ...
     end
-      
   end
+
   def test_assert_difference
-    @object.num = 0
-    
-    
-    assert_difference @object, :num, +1 do
-      @object.num = 1
+    assert_difference '@object.num', +1 do
+      @object.increment
     end
-      
   end
 
-  def test_methods_available
-    
-    assert self.respond_to?(:assert_difference)
-    assert self.respond_to?(:assert_no_difference)
-    
+  def test_assert_difference_with_implicit_difference
+    assert_difference '@object.num' do
+      @object.increment
+    end
   end
 
+  def test_arbitrary_expression
+    assert_difference '@object.num + 1', +2 do
+      @object.increment
+      @object.increment
+    end
+  end
+
+  def test_negative_differences
+    assert_difference '@object.num', -1 do
+      @object.decrement
+    end
+  end
 end