Passing options to Cargo

cargo-mutants runs cargo test to build and run tests. (With --check, it runs cargo check.) Additional options can be passed in three different ways: to all cargo commands; to cargo test only; and to the test binaries run by cargo test.

There is not yet a way to pass options only to cargo build but not to cargo test.

Feature flags

The --features, --all-features, and --no-default-features flags can be given to cargo-mutants and they will be passed down to cargo invocations.

For example, this can be useful if you have tests that are only enabled with a feature flag:

cargo mutants -- --features=fail/failpoints

Arguments to all cargo commands

To pass more arguments to every Cargo invocation, use --cargo-arg, or the additional_cargo_args configuration key. --cargo-arg can be repeated.

For example

cargo mutants -- --cargo-arg=--release

or in .cargo/mutants.toml:

additional_cargo_args = ["--all-features"]

Arguments to cargo test

Command-line options following a -- delimiter are passed through to cargo test (or to nextest, if you're using that).

For example, this can be used to pass --all-targets which (unobviously) excludes doctests. (If the doctests are numerous and slow, and not relied upon to catch bugs, this can improve performance.)

cargo mutants -- --all-targets

These options can also be configured statically with the additional_cargo_test_args key in .cargo/mutants.toml:

additional_cargo_test_args = ["--jobs=1"]

Arguments to test binaries

You can use a second double-dash to pass options through to the test targets:

cargo mutants -- -- --test-threads 1 --nocapture

(However, this may interact poorly with using additional_cargo_test_args in the configuration file, as the argument lists are currently appended without specially handling the -- separator.)