'An ``InvariantException`` is raised if a lease\'s ID (key in the
``Leases`` map) does not match its dataset ID.'

def test_invariant_fail(self):

    lease = Lease(dataset_id=self.dataset_id, node_id=self.node_id, expiration=None)
    self.assertRaises(InvariantException, self.leases.set, uuid4(), lease)
