Testing complex command structures without repeating App construction

[jburnett]

Rust newbie alert!

For complex command structures, how can I construct the handler once for multiple reuse? Testing the various commands and options would be much simpler using something like a singleton. A test would look a bit like the following (based on the example for Arg::last in clap docs for 2.33.1)

static MATCHER:  App = App::new("prog")
        .arg(Arg::with_name("first"))
        .arg(Arg::with_name("second"))
        .arg(Arg::with_name("third").last(true));

#[test]
fn verify_three_params() {
    let res = MATCHER.get_matches_from_safe(vec![
            "prog", "one", "--", "three"
    ]);

    assert!(res.is_ok());
    let m = res.unwrap();
    assert_eq!(m.value_of("third"), Some("three"));
    assert!(m.value_of("second").is_none());
}

Thanks in advance!

[kbknapp]

To test your CLI I would look into something like assert_cli or assert_cmd.

If you're wanting to do something closer to your example then I usually use a non-test function to setup the App instance each time. This is because setting up the App instance is very fast (ns fast), and during the parsing phase, it'll get mutated so it's best to start clean for each test. It would look something like:

fn build() -> App<'static, 'static> {
    App::new("prog")
        .arg(Arg::with_name("first"))
        .arg(Arg::with_name("second"))
        .arg(Arg::with_name("third").last(true))
}

#[test]
fn verify_three_params() {
    let res = build().get_matches_from_safe(vec![
            "prog", "one", "--", "three"
    ]);

    assert!(res.is_ok());
    let m = res.unwrap();
    assert_eq!(m.value_of("third"), Some("three"));
    assert!(m.value_of("second").is_none());
}

You can look in the tests/ dir of this repository as we do a lot of testing.