'Fail if the object is an instance of the specified classes.
Fail the test if the object ``obj`` is an instance of any
of ``classes``.'

def failIfIsInstance(self, obj, classes, msg=None):

    if isinstance(obj, classes):
        if (msg is None):
            msg = ('%(obj)r    is    an    instance    of    one    of    %(classes)r' % vars())
        raise self.failureException(msg)
