#562 WIP - Refactoring YouTube tests.

Refactoring tests as per the suggestions in #517.
- Comparing expected sample video metadata to metadata retrieved from video file.
- Tests to use parametrized test functions.

Closes #562 
I started reading the docs on the parametrized tests from the above link, and experimenting a little: It appears that mixing pytest's parametrized fixtures with unittest.TestCase methods isn't straight forward (it's noted at the bottom of this page: https://pytest.org/latest/unittest.html).

If I refactor these tests to completely use pytest instead of unittest, will the test scripts need to be modified in order to run them? Alternatively, I can continue to refactor these tests without use of pytest.