'L{SSHProcotolChecker.registerChecker} should add the given checker to
the list of registered checkers.'

def test_registerChecker(self):

    checker = checkers.SSHProtocolChecker()
    self.assertEqual(checker.credentialInterfaces, [])
    checker.registerChecker(checkers.SSHPublicKeyDatabase())
    self.assertEqual(checker.credentialInterfaces, [ISSHPrivateKey])
    self.assertIsInstance(checker.checkers[ISSHPrivateKey], checkers.SSHPublicKeyDatabase)
