0
@@ -15,6 +15,77 @@ module ThoughtBot # :nodoc:
0
           end
0
           fixtures *all_fixtures
0
         end
0
+        
0
+        # Macro that creates a test asserting a change between the return value
0
+        # of an expression that is run before and after the current setup block
0
+        # is run. This is similar to Active Support's <tt>assert_difference</tt>
0
+        # assertion, but supports more than just numeric values.  See also
0
+        # should_not_change.
0
+        #
0
+        # Example:
0
+        #
0
+        #   context "Creating a post"
0
+        #     setup do
0
+        #       Post.create
0
+        #     end
0
+        #
0
+        #     should_change "Post.count", :by => 1
0
+        #   end
0
+        #
0
+        # As shown in this example, the <tt>:by</tt> option expects a numeric
0
+        # difference between the before and after values of the expression.  You
0
+        # may also specify <tt>:from</tt> and <tt>:to</tt> options:
0
+        #
0
+        #   should_change "Post.count", :from => 0, :to => 1
0
+        #   should_change "@post.title", :from => "old", :to => "new"
0
+        #
0
+        # Combinations of <tt>:by</tt>, <tt>:from</tt>, and <tt>:to</tt> are allowed:
0
+        #
0
+        #   should_change "@post.title"                # => assert the value changed in some way
0
+        #   should_change "@post.title" :from => "old" # => assert the value changed to anything other than "old"
0
+        #   should_change "@post.title" :to   => "new" # => assert the value changed from anything other than "new"
0
+        def should_change(expression, options = {}) 
0
+          by, from, to = get_options!([options], :by, :from, :to)
0
+          stmt = "change '#{expression}'"
0
+          stmt << " from '#{from}'" if from
0
+          stmt << " to '#{to}'" if to
0
+          stmt << " by #{by}" if by
0
+
0
+          expression_eval = lambda { eval(expression) }
0
+          before = lambda do
0
+            @_before_should_change = expression_eval.bind(self).call
0
+            assert_equal from, @_before_should_change, "'#{expression}' was not originally '#{from}'" if from
0
+          end
0
+          should stmt, :before => before do
0
+            old_value = @_before_should_change
0
+            new_value = expression_eval.bind(self).call
0
+            assert_not_equal old_value, new_value, "'#{expression}' did not change" unless by == 0
0
+            assert_equal to, new_value, "'#{expression}' was not changed to '#{to}'" if to
0
+            assert_equal old_value + by, new_value if by
0
+          end
0
+        end
0
+        
0
+        # Macro that creates a test asserting no change between the return value
0
+        # of an expression that is run before and after the current setup block
0
+        # is run. This is the logical opposite of should_change.
0
+        #
0
+        # Example:
0
+        #
0
+        #   context "Updating a post"
0
+        #     setup do
0
+        #       @post.update_attributes(:title => "new")
0
+        #     end
0
+        #
0
+        #     should_not_change "Post.count"
0
+        #   end
0
+        def should_not_change(expression)
0
+          expression_eval = lambda { eval(expression) }
0
+          before = lambda { @_before_should_not_change = expression_eval.bind(self).call }
0
+          should "not change '#{expression}'", :before => before do
0
+            new_value = expression_eval.bind(self).call
0
+            assert_equal @_before_should_not_change, new_value, "'#{expression}' changed"
0
+          end
0
+        end
0
       end
0
       
0
       # Prints a message to stdout, tagged with the name of the calling method.

0
@@ -77,4 +77,35 @@ class HelpersTest < Test::Unit::TestCase # :nodoc:
0
       end
0
     end
0
   end
0
+  
0
+  context "an array of numbers" do
0
+    setup do
0
+      @a = [1, 2, 3]
0
+    end
0
+
0
+    context "after adding another value" do
0
+      setup do
0
+        @a.push(4)
0
+      end
0
+
0
+      should_change "@a.length", :by => 1
0
+      should_change "@a.length", :from => 3
0
+      should_change "@a.length", :to => 4
0
+      should_change "@a[0]", :by => 0
0
+      should_not_change "@a[0]"
0
+    end
0
+
0
+    context "after replacing it with an array of strings" do
0
+      setup do
0
+        @a = %w(a b c d e f)
0
+      end
0
+
0
+      should_change "@a.length", :by => 3
0
+      should_change "@a.length", :from => 3, :to => 6, :by => 3
0
+      should_change "@a[0]"
0
+      should_change "@a[1]", :from => 2, :to => "b"
0
+      should_change "@a[2]", :from => 3
0
+      should_change "@a[3]", :to => "d"
0
+    end
0
+  end
0
 end