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rjest

A blazing-fast, drop-in replacement for Jest.

rjest keeps a Rust daemon (jestd) running in the background, caching SWC transforms and pre-warming Node.js workers across test invocations. It reads your existing jest.config.* files with zero config changes and supports the same CLI flags you already use: --watch, --coverage, --runInBand, --testNamePattern, --json, --machine.

On the project's benchmark suite (136 TypeScript tests across 3 files in tests/fixtures/basic-ts), warm runs complete in ~100ms vs ~14,200ms for upstream Jest — a ~95x speedup. See BENCHMARK.md for raw numbers.

Why rjest?

Metric rjest Jest Speedup
Cold start (136 tests) 9.2s 14.2s 1.5x
Warm run (136 tests) ~100ms ~14.2s ~95x
Daemon resident memory ~17 MB — —
Total memory (daemon + 4 workers) ~212 MB ~108 MB +96%

Key Features

  • Jest-compatible — same CLI flags, matchers, snapshots, hooks, and jest.* globals
  • Zero config — reads jest.config.{js,ts,mjs,json} or the jest key in package.json
  • Native TypeScript / JSX — compiled in Rust via SWC; no Babel or ts-jest required
  • Persistent transform cache — content-hashed (blake3) results stored on disk in sled; survive daemon restarts
  • Pre-warmed worker pool — up to 4 Node.js workers stay hot across runs (idle workers recycled after 60s, all workers recycled after 1000 tests)
  • Structured output — --json and --machine flags for CI pipelines and AI agents
  • Drop-in fallback — --fallback-to-jest (or RJEST_FALLBACK=1) forwards to upstream Jest for unsupported edge cases

Install

# npm (recommended for Node.js projects)
npm install -D rjest-install

# Homebrew (macOS / Linux)
brew tap neul-labs/tap
brew install rjest

# Cargo (Rust toolchain)
cargo install rjest

# pip (Python ecosystem)
pip install rjest-install

See Installation for full instructions.

Quick Start

# Run all tests — daemon starts automatically on first use
npx rjest

# Watch mode
npx rjest --watch

# Filter by test name
npx rjest --testNamePattern="add"

# Structured output for CI and AI agents
npx rjest --json
npx rjest --machine

How it works

┌─────────────┐     IPC (nng over           ┌──────────────┐
│   jest CLI  │     Unix socket)            │    jestd     │
│  (rjest)    │ ◄──────────────────────────► │   (Rust)     │
└─────────────┘                              └──────┬───────┘
                                                    │
                          ┌─────────────────────────┼─────────────────────────┐
                          │                         │                         │
                     ┌────▼────┐               ┌────▼────┐               ┌────▼────┐
                     │ Worker 1│   ...         │ Worker 2│   ...         │ Worker N│
                     │ (Node)  │               │ (Node)  │               │ (Node)  │
                     └─────────┘               └─────────┘               └─────────┘
  1. First run — daemon spawns, parses config via Node, discovers tests, compiles files with SWC, warms workers.
  2. Subsequent runs — CLI re-connects over the existing Unix socket; cached transforms are reused; warm V8 returns results in ~100ms.

See Architecture for details.

Where to go next

License

MIT — see LICENSE.