'Check that we have a deprecation warning for C{objectType}.'

def checkDeprecation(self):

    warnings = self.flushWarnings()
    self.assertEqual(1, len(warnings))
    self.assertIs(DeprecationWarning, warnings[0]['category'])
    self.assertEqual('twisted.conch.ssh.keys.objectType    was    deprecated    in    Twisted    15.5.0', warnings[0]['message'])
