CONTRIBUTING.md in paperclip-3.0.2 vs CONTRIBUTING.md in paperclip-3.0.3

@@ -1,5 +1,8 @@
+Contributing
+============
+
 We love pull requests. Here's a quick guide:
 
 1. Fork the repo.
 
 2. Run the tests. We only take pull requests with passing tests, and it's great
@@ -11,11 +14,10 @@
 
 4. Make the test pass.
 
 5. Push to your fork and submit a pull request.
 
-
 At this point you're waiting on us. We like to at least comment on, if not
 accept, pull requests within three business days (and, typically, one business
 day). We may suggest some changes or improvements or alternatives.
 
 Some things that will increase the chance that your pull request is accepted,
@@ -24,10 +26,40 @@
 * Use Rails idioms and helpers
 * Include tests that fail without your code, and pass with it
 * Update the documentation, the surrounding one, examples elsewhere, guides,
   whatever is affected by your contribution
 
-Syntax:
+Running Tests
+-------------
+
+Paperclip uses [Appraisal](https://github.com/thoughtbot/appraisal) to aid
+testing against multiple version of Ruby on Rails. This helps us to make sure
+that Paperclip performs correctly with them.
+
+### Bootstrapping your test suite:
+
+    bundle install
+    bundle exec rake appraisal:install
+
+This will install all the required gems that requires to test against each
+version of Rails, which defined in `gemfiles/*.gemfile`.
+
+### To run a full test suite:
+
+    bundle exec rake
+
+This will run Test::Unit and Cucumber against all version of Rails
+
+### To run single Test::Unit or Cucumber test
+
+You need to specify a `BUNDLE_GEMFILE` pointing to the gemfile before running
+the normal test command:
+
+    BUNDLE_GEMFILE=gemfiles/3.2.gemfile ruby -Itest test/schema_test.rb
+    BUNDLE_GEMFILE=gemfiles/3.2.gemfile cucumber features/basic_integration.feature
+
+Syntax
+------
 
 * Two spaces, no tabs.
 * No trailing whitespace. Blank lines should not have any space.
 * Prefer &&/|| over and/or.
 * MyClass.my_method(my_arg) not my_method( my_arg ) or my_method my_arg.