autospy

🎵 autospy record, autospy replace 🎵

A test spy object library.

Overview

Spies are a type of test double used for unit testing software. A test spy is an object providing the same interface as the production code, but which allows setting of the output before a test runs and verification of input parameters after the test run.

#[autospy] generates a test spy object for traits.

Usage

Spy objects are often only used by unit tests, the example below demonstrates use in a unit test assuming included in [dev-dependencies].

#![allow(unused)]
fn main() {
#[cfg(test)]
use autospy::autospy;

#[cfg_attr(test, autospy)]
trait MyTrait {
    fn foo(&self, x: u32) -> bool;
}

fn use_trait(trait_object: impl MyTrait) -> bool {
    trait_object.foo(10)
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_trait() {
        let spy = MyTraitSpy::default();
        spy.foo.returns.push_back(true);

        assert!(use_trait(spy.clone()));
        assert_eq!(vec![10], spy.foo.arguments.take_all())
    }
}
}

For additional examples and features see the docs.

Acknowledgements

Autospy is heavily influenced by the excellent mockall crate, which through automock provides much the same features. Autospy aims to offer these same features through a macro generated spy object, rather than a mock object. The use of either is largely personal preference; however, there are some benefits to using a spy object. Notably, a mock object will panic if its expectations fail which can cause less legible error messages.