#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 
Yeah, I definitely wouldn't mix the two styles.

You could start by refactoring the testcases that would benefit from parametrization into new top-level functions (aka pytest style).