def METHOD_NAME(self):
    source = "Subject: test\n\ntest body\n"
    expected = source
    msg = self.msgmaker(self.typ(source))
    s = self.ioclass()
    g = self.genclass(s, policy=policy.SMTP)
    g.flatten(msg, linesep='\n')
    self.assertEqual(s.getvalue(), self.typ(expected))