Testing exception in plugin

[onosendi]

What's the proper way to test if an exception is thrown in a plugin?

async function myPlugin(fastify, config) {
  if (config === 'foo') {
    throw new Error('foo');
  }

  fastify.decorate('foo', 'foo');
}

test('Throws foo', () => {
  const fastify = Fastify();

  // This doesn't work.
  expect(() => {
    fastify.register(myPlugin, 'foo');
  }).toThrow();
});

[Uzlopak]

With tap it would be

await t.rejects(() => fastify.register(myPlugin, 'foo'), new Error('foo'))

You are using mocha/chai. So read the documentation of your test runner on how to test for promises and rejections.
e.g. https://www.chaijs.com/plugins/chai-as-promised/

[onosendi]

I'm doing:

test('', async () => {
  try {
    await fastify.register(myPlugin, 'foo');
  } catch (e) {
    expect(e.message).toBe('foo');
  }
});

[onosendi]

Oh, hmm, I see what you're saying.

[Uzlopak]

test('', async () => {
  try {
    await fastify.register(myPlugin, 'foo');
    fail('should have thrown');
  } catch (e) {
    expect(e.message).toBe('foo');
  }
});

Thats why you should use rejects.
https://jestjs.io/docs/expect#rejects

[onosendi]

Ah, yes. rejects/resolves is a lot cleaner. Thank you.

[onosendi]

If anyone else comes across this:

test('', async () => {
  await expect(fastify.register(myPlugin, 'foo'))
    .rejects
    .toThrow('foo');
});