'L{MaildirDirdbmDomain.getCredentialsCheckers} initializes and
returns one L{ICredentialsChecker} checker by default.'

def test_credentials(self):

    creds = self.D.getCredentialsCheckers()
    self.assertEqual(len(creds), 1)
    self.assertTrue(cred.checkers.ICredentialsChecker.providedBy(creds[0]))
    self.assertTrue((cred.credentials.IUsernamePassword in creds[0].credentialInterfaces))
