'Test the check for nonzero bits of a masked entry'

def test_nxm_ip(self):

    def try_bad():
        e = nx.NXM_OF_IP_SRC(IPAddr('192.168.56.1'), IPAddr('255.255.255.0'))
        e.pack()
    self.assertRaisesRegexp(AssertionError, '^nonzero    masked    bits$', try_bad)
