'Test that trying to download a message with a bad argument, either not
an integer or an out-of-bounds integer, fails with the appropriate
error response.'

def testRETRWithBadArgument(self):

    p = self.pop3Server
    s = self.pop3Transport
    p.lineReceived('RETR    a')
    self.assertEqual(s.getvalue(), '-ERR    Bad    message    number    argument\r\n')
    s.truncate(0)
    p.lineReceived('RETR    0')
    self.assertEqual(s.getvalue(), '-ERR    Bad    message    number    argument\r\n')
    s.truncate(0)
    p.lineReceived('RETR    2')
    self.assertEqual(s.getvalue(), '-ERR    Bad    message    number    argument\r\n')
    s.truncate(0)
