1. Include all fields in _TEST 2. Use .get() for optional fields 3. Clarify the intention of 'ext' in formats
For example with 'best[height<40]' we ended getting a 'IndexError: list index out of range'.
When using 'bestvideo/best,bestaudio', 'bestvideo/best' must be set as the current_selector (instead of appending it to the selectors), otherwise when it gets the ',' it would append 'None' to the selectors.
Python 2.x does not work without it.