Test XState logic

Test observable behavior: the event sent, the resulting snapshot and effects at system boundaries.

test('pauses while playing', () => {
  const player = createActor(playerMachine).start();
  player.send({ type: 'play' });
  player.send({ type: 'pause' });
  expect(player.getSnapshot().matches('paused')).toBe(true);
});

Test forbidden behavior too.

test('does not pause while stopped', () => {
  const player = createActor(playerMachine).start();
  player.send({ type: 'pause' });
  expect(player.getSnapshot().matches('stopped')).toBe(true);
});

Use waitFor(...) for async outcomes. Provide fake actor logic for network, clock and storage boundaries.

Use getInitialSnapshot(...) and getNextSnapshot(...) when a test only needs pure transition results. Start an actor when the test covers effects, child actors or subscriptions.

For an order workflow, test the successful payment path and a declined payment retry. For an upload, test completion and cancellation while the request is active.