Improve the PhabricatorInfrastructureTestCase unit tests
Summary:
Improve the PhabricatorInfrastructureTestCase unit tests such that they will fail if any of the following conditions are satisfied:
- A symbol referenced in the __phutil_library_map__.php file no longer exists.
- A symbol exists in the library but is not referenced within the __phutil_library_map__.php file.
- A symbol extends from a different parent symbol than that declared in the __phutil_library_map.php file.
Test Plan: See D9824.
Reviewers: Blessed Reviewers, epriestley
Reviewed By: Blessed Reviewers, epriestley
Subscribers: epriestley, Korvin
Differential Revision: https://secure.phabricator.com/D9827