feat(testing): expose ConfigFile in testing API

[simonsan]

For testing purposes, it would be useful, to have the testing::config::ConfigFile struct being exposed.

For example I can't use the internal CmdRunner, also because it doesn't support searching in command output ergonomically. So I use assert_cmd, but I like the ease of use of my config being serialized and injected in the call to the command runner, so I implemented:

pub trait AssertCmdExt {
    /// Add the given configuration file
    fn config(&mut self, config: &impl Serialize) -> &mut Self;
}

impl AssertCmdExt for Command {
    fn config(&mut self, config: &impl Serialize) -> &mut Self {
        let target_bin = self.get_program().to_owned();

        let config_file = ConfigFile::create(&target_bin, config);

        // Leak the config file to keep it alive for the duration of the test
        let static_config: &'static mut ConfigFile = Box::leak(Box::new(config_file));

        self.args(&["-c", &static_config.path().display().to_string()]);
        self
    }
}

/// Use configured value
#[rstest]
fn start_with_config_no_args(setup: Result<Command>) -> Result<()> {
    let mut config = RusticServerConfig::default();
    config.server.listen = SocketAddr::from(([127, 0, 0, 1], 8081));

    let assert = setup?.config(&config).arg("serve").arg("-v").assert();

    assert
        .stdout(predicates::str::contains("listen: 127.0.0.1:8081"))
        .success();

    Ok(())
}

So can we expose the ConfigFile in the public API for testing, please? 🙏🏽

[simonsan]

If another approach would be more interesting, e.g. exposing some more functionality around that, to not need to leak the Config file (so it can be removed within the drop impl from the temp files), let me know.