def METHOD_NAME(self, mock_open):
    flh = outwin.file_line_helper
    test_lines = (
        (r'foo file "testfile1", line 42, bar', ('testfile1', 42)),
        (r'foo testfile2(21) bar', ('testfile2', 21)),
        (r'  testfile3  : 42: foo bar\n', ('  testfile3  ', 42)),
        (r'foo testfile4.py :1: ', ('foo testfile4.py ', 1)),
        ('testfile5: \u19D4\u19D2: ', ('testfile5', 42)),
        (r'testfile6: 42', None),       # only one `:`
        (r'testfile7 42 text', None)    # no separators
        )
    for line, expected_output in test_lines:
        self.assertEqual(flh(line), expected_output)
        if expected_output:
            mock_open.assert_called_with(expected_output[0], 'r')