def test_openWithRedundantExplicitBinaryModes(self):
        """
        Due to a bug in Python 2.7 on Windows including multiple 'b'
        characters in the mode passed to the built-in open() will cause an
        error.  No matter how many 'b' modes are specified, FilePath.open()
        ensures that only a single 'b' character is included in the mode
        passed to the built-in open().

        See http://bugs.python.org/issue7686 for details about the bug.
        """
        writer = self.path.child(b'multiple-binary')
        with writer.open('wbb') as file:
            file.write(b'abc\ndef')
        self.assertTrue(writer.exists)

        Due to a bug in Python 2.7 on Windows including multiple 'b'
        characters in the mode passed to the built-in open() will cause an
        error.  No matter how many 'b' modes are specified, FilePath.open()
        ensures that only a single 'b' character is included in the mode
        passed to the built-in open().

        See http://bugs.python.org/issue7686 for details about the bug.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_paths.py