'L{PLAINCredentials.setResponse} raises L{imap4.IllegalClientResponse}
when passed a string not of the expected form.'

def test_credentialsInvalidResponse(self):

    cred = imap4.PLAINCredentials()
    self.assertRaises(imap4.IllegalClientResponse, cred.setResponse, 'hello')
    self.assertRaises(imap4.IllegalClientResponse, cred.setResponse, 'hello\x00world')
    self.assertRaises(imap4.IllegalClientResponse, cred.setResponse, 'hello\x00world\x00Zoom!\x00')
