Glossary
The vocabulary of rjest
rjest borrows a lot of Rust and V8 vocabulary. Here is what each term means in the context of the runner.
- jestd
- The rjest daemon. A persistent Rust process that holds the parsed Jest config, the dependency graph, the file-system watcher, and the warm worker pool between invocations.
- Warm run
- A test run served by an already-running daemon with a populated cache and warm workers. This is the path where rjest is 10–100x faster than Jest.
- Cold start
- The first run in a session, where the daemon must boot and workers must warm up. rjest is honestly a little slower here (~1.9s vs Jest ~1.4s in the repo benchmark); the cost is paid once.
- SWC
- A Rust-based platform for compiling JavaScript and TypeScript. rjest uses SWC to transform TS and JSX natively, avoiding Babel and ts-jest.
- sled
- An embedded, transactional key-value store written in Rust. rjest uses it to persist transformed modules on disk so the cache survives daemon restarts.
- blake3
- A fast cryptographic hash. rjest keys its transform cache by the blake3 hash of a file's source bytes, so a module only re-transforms when its content actually changes.
- nng
- nanomsg-next-gen, a lightweight messaging library. rjest uses it over a Unix domain socket for sub-millisecond communication between the CLI and the daemon.
- VM context
- An isolated V8 execution context. Each test file runs in its own VM context inside a warm Node.js worker, keeping tests isolated without a fresh process per file.
- Worker pool
- The set of persistent Node.js processes the daemon keeps alive. Tests schedule onto already-JITed workers instead of forking a new process per run.
- Compatibility contract
- The set of Jest behaviors rjest commits to honoring — matchers, mocks, snapshots, fake timers, config files, and CLI flags. If Jest passes and rjest does not, that is a bug.
- --machine output
- A structured, stable output mode (alongside --json) designed for AI coding agents and CI parsers that need to read results without scraping ANSI-colored text.
- Transform cache
- The on-disk store of compiled TS/JSX output. Content-addressed by blake3, it lets rjest skip re-compiling unchanged files across runs and across daemon restarts.