Install cargo-mutants from source:
cargo install --locked cargo-mutants
Building cargo-mutants requires a reasonably recent stable (or nightly or beta) Rust toolchain. The supported version is visible in https://crates.io/crates/cargo-mutants.
After installing cargo-mutants, you should be able to use it to run tests under
any toolchain, even toolchains that are far too old to build cargo-mutants, using the standard
+ option to
cargo +1.48 mutants