testing.md

Testing

Pure transition paths

Use simulate for a complete event list:

const result = yield * simulate(machine, events, { input });
expect(result.states.map((state) => state._tag)).toEqual(["Idle", "Loading", "Done"]);

Use createTestHarness when each step needs an assertion. Use assertPath, assertReaches, and assertNeverReaches for invariant-style tests.

Simulation and replay run pure or Effectful transition handlers. They do not run tasks, state-owned Effects, background Effects, or timeouts. Their self operations are inert.

Runtime behavior

Spawn a real actor when a test covers services, tasks, child actors, persistence, supervision, inspection, or cleanup.

Provide test services through Effect:

it.scopedLive("loads the order", () => program.pipe(Effect.provide(OrderRepositoryTest)));

Use TestClock for timeouts and schedules. Use Deferred, Latch, Queue, Ref, or a test service hook for concurrent ordering. Do not use an arbitrary sleep to guess that work has started.

UI performance

Test the public rendering behavior:

• Count component renders in React.
• Count selected reactive computations in Solid.
• Change one field at a time.
• Assert that unrelated selections do not update.
• Assert that the changed selection updates once.

The repository runs these checks in both browser example packages.