openair: Simplified path constants in unit tests
openair: Renamed assert_record() to assert_line()
openair: Added category comments to unit test
openair: Fixed flake8 issues
openair: Moved State subclass to the bottom
openair: Extracted State.add_element() method
openair: Replaced warnings array with (result, error) generator
openair: Call handle_line() only if there is a valid record
openair: Renamed block property to record
openair: Fixed broken unit test