Faster Rust Testing at Scale: cargo-nextest in Practice
In a Nutshell
Rain created cargo-nextest to solve the speed and observability problems that cargo test faces with large Rust test suites, delivering up to 3x faster execution through process-per-test isolation, built-in retries, and rich configuration. The tool's most powerful recent features are full-fidelity test recording for CI replay and first-class debugger integration that preserves environment setup. The underlying philosophy emphasizes handling every failure mode—crashes, signals, resource exhaustion—rather than just the happy path, which is why roughly 80% of the codebase addresses error cases.
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Vitaly introduces the RustRover livestream series and announces RustRover's implementation of support for cargo nextest. Rain, the author of cargo nextest, is the guest speaker. A link to the RustRover blog post about the implementation is available in the video description.
Rain is a software engineer with 14-15 years of industry experience. Originally from India, Rain has been based in the San Francisco Bay Area since 2012. Career history includes work as a contractor at Mozilla, 10 years at Facebook/Meta, and currently at Oxide Computer Company. Rain has been writing Rust professionally since 2017, representing 9.5 years of professional Rust experience.
Cargo nextest is described as a next-generation test runner for Rust. Benchmarks show it can be up to three times faster than cargo test. Features include flaky test detection, JUnit output, handling of tests that terminate abnormally including segfaults, a rich configuration language allowing per-test configuration, retries, and recording runs for playback in CI. The tool has strong CI focus while also addressing local interactive developer experience.
Rain's first computer was an old 386. At around age 6, Rain began exploring the computer and discovered a book on GW Basic in their father's bookshelf. This led to writing simple programs and falling in love with programming at a young age. Rain later pursued a CS degree and has continued programming professionally.
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