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Argus

Quick start

  1. Install the runner.

    Terminal window
    pnpm add -D @argus/cli

  2. Write a test. No import of the test API is needed — describe, test, it, expect and the hooks are installed as globals inside the Hermes realm.

    src/money.test.ts
    import { formatCents } from './money';
    

    describe('formatCents', () => {
      test('formats whole euros', () => {
        expect(formatCents(1200)).toBe('12.00');
      });
    

      test('rounds half up', () => {
        expect(formatCents(1205)).toBe('12.05');
      });
    

      test('rejects a negative amount', () => {
        expect(() => formatCents(-1)).toThrow(RangeError);
      });
    });

  3. Run it.

    Terminal window
    pnpm exec argus "src/**/*.test.ts"
    ✓ hermes v1 hermes-v250829098.0.16 · prebuilt darwin-arm64 · ~/.argus/cache/…/bin/hermes
    

    formatCents
      ✓ formats whole euros
      ✓ rounds half up
      ✓ rejects a negative amount
    

    3 passed, 0 failed, 0 todo, 3 total (41 ms in Hermes)
    

    1 files: 1 passed, 0 failed
    3 tests: 3 passed, 0 failed, 0 todo

  4. Break it on purpose, so you can see what a failure looks like.

    test('rounds half up', () => {
      expect(formatCents(1205)).toBe('12.06'); // wrong
    });
    formatCents
      ✓ formats whole euros
      ✗ rounds half up  — expected "12.06" but received "12.05"
        at src/money.test.ts:8:34
      ✓ rejects a negative amount
    

    2 passed, 1 failed, 0 todo, 3 total (39 ms in Hermes)

    The frame says src/money.test.ts:8, not run.argus-bundle.js:2418. Stacks are remapped through the bundle’s source map before anything is printed — see Source maps.

  5. Add it to package.json so it runs like any other check.

    package.json
    {
      "scripts": {
        "test:hermes": "argus \"src/**/*.test.ts\" \"src/**/*.test.tsx\""
      }
    }

What just happened

Section titled “What just happened”

For that one file, Argus:

  1. Read node_modules/react-native to find which Hermes engine and version your project pins.
  2. Resolved a binary for it — cache, then the published prebuilt, verifying its checksum.
  3. Bundled the test and its imports into a single sealed IIFE, lowered to the Hermes syntax envelope, with an external source map.
  4. Spawned hermes on that file, in its own process.
  5. Read back exactly one framed result line carrying a private per-run nonce.
  6. Remapped every stack frame to your source, and rendered the report.

Where to go next

Section titled “Where to go next”