Deploy/Simpletest causes fatal PHP error - Class 'DeployWebTestCase' not found

Steps to reproduce:

• Install Drupal 7
• Download deploy
• Enable simpletest
• Navigate to /admin/config/development/testing
• Get a fatal PHP error: "PHP Fatal error: Class 'DeployWebTestCase' not found in /var/www/html/htdocs/profiles/projectx/modules/contrib/deploy/deploy.test on line 11"

This happens because simpletest includes .test files from disabled modules so that all tests (of enabled and disabled modules) are available, since the classes in deploy.test extend a class (DeployWebTestCase) in deploy_web_test_case.php which is not included by simpletest (or by any other means) the fatal error occurs.

I've attached a patch which moves the DeployWebTestCase code into deploy.test, this is one approach, another approach maybe preferable.