def is_wpt_idlharness_test(test_file):
        """Returns whether a WPT test is (probably) an idlharness test.

        There are no rules in WPT that can be used to identify idlharness tests
        without examining the file contents (which would be expensive). This
        method utilizes a filename heuristic, based on the convention of
        including 'idlharness' in the appropriate test names.
        """
        match = Port.WPT_REGEX.match(test_file)
        if not match:
            return False
        filename = match.group(2).split('/')[-1]
        return 'idlharness' in filename