Some ideas

Great start at unit testing! Here are just a few changes I made

* Use a different namespace for tests (PSR-0 compliance)
* Added code coverage to aide while testing for various code paths
* Separate tests for all code paths (be explicit)
  * I moved the initial tests in `testRetrieveAnnotationsFromString`, `testRetrieveDescriptionFromString` into their own test cases for better clarity.

Recommendations:
* A quick sanity check is to run `vendor/bin/phpunit --testdox` and see if the test suite makes sense. If not, then change it.
* Try not to use multiple assertions whos assertion is already covered by another (assertArrayHasKey and assertEquals).
* No need to unset local variables at the end (`$annotationExpected`, `$descriptionExpected`, `$result`)

This was just a quick pass, letme know what you think!