def METHOD_NAME(self):
    self.useFixture(
        fixture_setup.SnapcraftYaml(
            self.path,
            base="core18",
            parts={"part1": {"source": ".", "plugin": "nil"}},
        )
    )
    result = self.run_command(["help", "python", "--base", "core20"])
    expected = (
        "Displaying help for the 'python' plugin for 'core20'.\n\n"
        "The python plugin can be used for"
    )
    output = result.output[: len(expected)]
    self.assertThat(
        output,
        Equals(expected),
        "The help message does not start with {!r} but with "
        "{!r} instead".format(expected, output),
    )