def assertIsNot(self, first, second, msg=None):
        """
        Fail the test if C{first} is C{second}.  This is an
        obect-identity-equality test, not an object equality
        (i.e. C{__eq__}) test.

        @param msg: if msg is None, then the failure message will be
        '%r is %r' % (first, second)
        """
        if first is second:
            raise self.failureException(msg or '%r is %r' % (first, second))
        return first

        Fail the test if C{first} is C{second}.  This is an
        obect-identity-equality test, not an object equality
        (i.e. C{__eq__}) test.

        @param msg: if msg is None, then the failure message will be
        '%r is %r' % (first, second)
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/trial/_synctest.py