Update contributing guidelines.

CONTRIBUTING.md

@@ -114,25 +114,29 @@ project:
    $ git checkout -b <topic-branch-name>
    ```
 
-4. Commit your changes in logical chunks. Please adhere to these [git commit
+4. Add relevant tests to cover the change.
+
+5. Make sure test-suite passes: `npm test`
+
+6. Commit your changes in logical chunks. Please adhere to these [git commit
    message guidelines](http://tbaggery.com/2008/04/19/a-note-about-git-commit-messages.html)
    or your code is unlikely be merged into the main project. Use Git's
    [interactive rebase](https://help.github.com/articles/interactive-rebase)
    feature to tidy up your commits before making them public.
 
-5. Locally merge (or rebase) the upstream development branch into your topic branch:
+7. Locally merge (or rebase) the upstream development branch into your topic branch:
 
    ```bash
    $ git pull [--rebase] upstream <dev-branch>
    ```
 
-6. Push your topic branch up to your fork:
+8. Push your topic branch up to your fork:
 
    ```bash
    $ git push origin <topic-branch-name>
    ```
 
-7. [Open a Pull Request](https://help.github.com/articles/using-pull-requests/)
+9. [Open a Pull Request](https://help.github.com/articles/using-pull-requests/)
     with a clear title and description.
 
 ## Conventions of commit messages