如何从使用mockall模拟的方法中返回self？

Question

考虑到以下使用mockall库的测试上下文，我怎样才能令人满意地返回对

cmd

的引用，这将允许我对随后的链接方法调用做出断言？

mock! {
    Cmd {}
    impl CustomCommand for Cmd {
        fn args(&mut self, args: &[String]) -> &mut Self;
        fn output(&mut self) -> std::io::Result<Output>;
        fn spawn(&mut self) -> std::io::Result<std::process::Child>;
        fn status(&mut self) -> std::io::Result<ExitStatus>;
    }
}

#[test]
fn test_x() {
    let mut cmd = MockCmd::new();
    
    cmd.expect_args().times(1).returning(|_| &mut cmd);
    // results in:
    // expected `MockCmd`, found `&mut MockCmd`
    
    cmd.expect_args().times(1).returning(|_| cmd);
    // results in:
    // move occurs because `cmd` has type `tests::MockCmd`, which does not implement the `Copy` trait 
    // NOTE: I don't think I _can_ implement Copy for my struct because it's a newtype on top of Command

    cmd.expect_output()
        .times(1)
        .returning(|| Ok(create_output(0, vec![], vec![])));

    // Call the methods in the desired order
    let args = vec![String::from(":P")];
    let _x = cmd.args(&args).output();
}

Answer 1

这是不可能的，请参阅问题#106。正如本期所建议的，您可以做的最接近的事情是返回第二个

MockCmd

并对其设定期望。不过，这确实意味着您期望调用方法的特定顺序。如果这对您来说还不够好，您可以在

mockall

的存储库中打开问题。

#[test]
fn test_x() {
    let mut cmd = MockCmd::new();

    cmd.expect_args().once().returning(|_| {
        let mut cmd = MockCmd::new();
        cmd.expect_output()
            .once()
            .returning(|| Ok(create_output(0, vec![], vec![])));
        cmd
    });

    // Call the methods in the desired order
    let args = vec![String::from(":P")];
    let _x = cmd.args(&args).output();
}