def test_usage_error_message(self):
        fake_sys_module = FakeSysModule(argv=[])
        script = BuildScript(sys_module=fake_sys_module)

        try:
            script.main(top_level=FLOCKER_PATH)
        except SystemExit:
            pass
        self.assertEqual(
            'Wrong number of arguments.',
            fake_sys_module.stderr.getvalue().splitlines()[-1]
        )
``BuildScript.main`` prints a usage error to ``stderr`` if there are
dataset/ETHPy150Open ClusterHQ/flocker/admin/test/test_packaging.py/BuildScriptTests.test_usage_error_message