Getting started

Just run cargo mutants in a Rust source directory, and it will point out functions that may be inadequately tested.

Prerequisites

For cargo-mutants to give useful results, your tree must already have reliable non-flaky tests that run under either cargo test or cargo nextest.

If the tests are flaky, meaning that they can pass or fail depending on factors other than the source tree, then the cargo-mutants results will be meaningless.

Cross-compilation is not currently supported, so the tree must be buildable for the host platform.

Build tools other than Cargo are not supported today, but could in principle be added.

Example

; cargo mutants
Found 14 mutants to test
Copy source to scratch directory ... 0 MB in 0.0s
Unmutated baseline ... ok in 1.6s build + 0.3s test
Auto-set test timeout to 20.0s
src/lib.rs:386: replace <impl Error for Error>::source -> Option<&(dyn std::error::Error + 'static)>
 with Default::default() ... NOT CAUGHT in 0.6s build + 0.3s test
src/lib.rs:485: replace copy_symlink -> Result<()> with Ok(Default::default()) ...
 NOT CAUGHT in 0.5s build + 0.3s test
14 mutants tested in 0:08: 2 missed, 9 caught, 3 unviable

In v0.5.1 of the cp_r crate, the copy_symlink function was reached by a test but not adequately tested, and the Error::source function was not tested at all.