Finds all of the (fixture_path, fixture_key) pairs for a given path under
    the JSON test fixtures directory.

def find_fixtures(fixtures_base_dir: str) -> Iterable[Tuple[str, str]]:
    """
    Finds all of the (fixture_path, fixture_key) pairs for a given path under
    the JSON test fixtures directory.
    """
    all_fixture_paths = find_fixture_files(fixtures_base_dir)

    for fixture_path in sorted(all_fixture_paths):
        with open(fixture_path) as fixture_file:
            fixtures = json.load(fixture_file)

        for fixture_key in sorted(fixtures.keys()):
            yield (fixture_path, fixture_key)