Half Sleep -- Mutation Testing For Rust

Half Sleep is a syntax extension for Rust which provides simple mutation testing. Mutation testing is a testing methodology in which functions are modified in simple but breaking ways. If the unit tests still pass, they weren't sufficient.

Rust's syntax extension abilities are powerful enough to do this without the need for any additional tools. The way it works is as follows: on any modules marked #[mutation_test], it finds functions marked #[mutate] and creates copies of them which are mutated in various ways. Then any unit tests in the module which call those functions are duplicated to use the mutated variant and marked #[should_panic] under the expectation that they will now fail. (Any tests already marked #[should_panic] are ignored rather than duplicated.)

Experimental and Unstable

This library is still quite new and subject to rapid change. Pull requests and feature suggestions are welcome.

Compiling

To use halfsleep in your project, add to your Cargo.toml

[dependencies.halfsleep]
git = "https://github.com/apoelstra/halfsleep.git"

Use

Here is an example project using halfsleep:

#![feature(custom_attribute, plugin)]

#![plugin(halfsleep)]
#![cfg_attr(test, mutation_test)]

#[mutate]
pub fn keep_fours(n: u32) -> u32 {
    if n == 4 { 4 } else { 100 }
}

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

    #[test]
    fn bad_test() {
        assert_eq!(keep_fours(4), 4);
    }
}

After running cargo test on this project, we get the output

running 4 tests
test tests::bad_test ... ok
test tests::_should_panic_bad_test_mutated_for_mutate_ifswap_keep_fours ... ok
test tests::_should_panic_bad_test_mutated_for_mutate_iffalse_keep_fours ... ok
test tests::_should_panic_bad_test_mutated_for_mutate_iftrue_keep_fours ... FAILED

We see that our single unit test has become four, and that the iftrue one has failed. This means that even after replacing if n == 4 with if true the unit test passed, so our unit test was not testing the if statement completely.