Make mutation stand out some more.

Felt that += overwriting the path variable was a little too hidden.

Make the outcomes easier to spot with an if-else branch.

Author: kaspth

actionpack/lib/action_dispatch/testing/integration.rb

@@ -423,8 +423,11 @@ def initialize(mime_name, param_encoder, response_parser, url_encoded_form = fal
           end
 
           def append_format_to(path)
-            path += @path_format unless @url_encoded_form
-            path
+            if @url_encoded_form
+              path + @path_format
+            else
+              path
+            end
           end
 
           def content_type