Jasmine async test reliability: unhandled promise rejections not consistently captured

Answer

Starting with Jasmine 2.0, a test that returns a rejected promise (or an async function that throws/rejects) is automatically marked as failed. Jasmine 1.x and earlier do not have this behavior; you must use the done callback and call done.fail on rejections.

Likely explanation

If a promise is rejected but the test function neither returns that promise nor awaits it, the rejection becomes an unhandled promise. Jasmine’s test runner does not automatically convert such global rejections into spec failures, so the rejection may appear as a console warning or Node UnhandledPromiseRejectionWarning instead.

Confirmed facts

• Jasmine 2.0 introduced native promise support: returning a promise from an it block causes the runner to wait for it and treat any rejection as a failure.
• Because an async function implicitly returns a promise, using async/await works the same way – the rejection is caught and the spec fails.
• When using the done callback, you must explicitly call done.fail(err) in a .catch handler (or try/catch) to turn a rejection into a failure; otherwise the test finishes silently.

Steps to make the rejection cause a test failure

1. Prefer returning the promise or using async/await:

it('should fail on rejection', async () => {
  await promiseThatRejects();
});

2. If you must use done, attach a catch handler:

it('should fail on rejection', (done) => {
  promiseThatRejects().catch(err => done.fail(err));
});

3. Alternatively, wrap async code in try/catch with done:

it('should fail on rejection', (done) => {
  try {
    await promiseThatRejects();
    done();
  } catch (e) {
    done.fail(e);
  }
});

Environment or configuration factors that surface the rejection as a global error

• Using done without handling the rejection (no .catch(done.fail) or try/catch).
• Returning a promise but then also calling done (causing the test to finish twice) – the runner may ignore the promise result.
• Running in an environment where the global unhandled‑rejection hook is enabled (Node ≥ 1.0, modern browsers) – the warning appears regardless of Jasmine’s handling.
• No Jasmine configuration flag changes this behavior; the runner’s promise handling is fixed.

Flag or API to force automatic failure on any unhandled promise rejection

Jasmine does not provide a flag or API that automatically treats every global unhandled promise rejection as a test failure. Reliability must be achieved by ensuring the test either returns/awaits the promise or uses done.fail as shown above.