'Verify that we can obtain bytes from rand_bytes() and
that they are different each time.  Test the parameter
of rand_bytes() for bad values.'

def test_bytes(self):

    b1 = rand.bytes(50)
    self.assertEqual(len(b1), 50)
    b2 = rand.bytes(num_bytes=50)
    self.assertNotEqual(b1, b2)
    b3 = rand.bytes(num_bytes=0)
    self.assertEqual(len(b3), 0)
    exc = self.assertRaises(ValueError, rand.bytes, (-1))
    self.assertEqual(str(exc), 'num_bytes    must    not    be    negative')
