Miri and nextest¶
Nextest works with the Miri interpreter for Rust. This interpreter can check for certain classes of undefined behavior. It can also run your tests for (almost) arbitrary targets.
Benefits¶
The main benefit of using nextest with Miri is that each test runs in its own process. This has several advantages:
- Miri itself is single-threaded, so
cargo miri test, which runs several tests in the same process, is also single-threaded. But nextest can run Miri tests in parallel, leading to test runs up to 3-4x faster. - Each test gets a separate Miri context, which can make it easier to perform operations like identifying memory leaks.
Note, however, that cargo miri test is able to detect data races where two tests race on a shared resource. Miri with nextest will not detect such races.
Usage¶
After installing Miri, run:
cargo miri nextest run
You may need to specify the toolchain to run as, using cargo +nightly-YYYY-MM-DD miri nextest run.
Miri supports cross-interpretation, so e.g. to run your tests on a big-endian target, run:
cargo miri nextest run --target mips64-unknown-linux-gnuabi64
This does not require installing any special toolchain, and will work even if you are using macOS or Windows.
Note: Archiving and reusing builds is not supported under Miri.
Configuring nextest running under Miri¶
If nextest detects a Miri environment, it uses the default-miri profile by default. Add repository-specific Miri configuration to this profile. For example, to terminate tests after 2 minutes, add this to .config/nextest.toml:
.config/nextest.toml[profile.default-miri]
slow-timeout = { period = "60s", terminate-after = 2 }