'Fail the test if :py:data:`containee` is not found in :py:data:`container`.
:param containee: the value that should be in :py:class:`container`
:param container: a sequence type, or in the case of a mapping type,
will follow semantics of \'if key in dict.keys()\'
:param msg: if msg is None, then the failure message will be
\'%r not in %r\' % (first, second)'

def failUnlessIn(self, containee, container, msg=None):

    if (containee not in container):
        raise self.failureException((msg or ('%r    not    in    %r' % (containee, container))))
    return containee
