Spies, Async Testing & the Ecosystem

Spies — Built-in Mocking

spyOn(userRepo, 'findById').and.returnValue({ id: 1, name: 'Ada' });
spyOn(logger, 'log').and.callThrough();   // still runs the real logger too
spyOn(emailService, 'send').and.callFake(() => Promise.resolve());

expect(userRepo.findById).toHaveBeenCalledWith(1);

// standalone spy, e.g. for a callback argument
const onComplete = jasmine.createSpy('onComplete');
runTask(onComplete);
expect(onComplete).toHaveBeenCalled();

// fake a whole dependency with several methods at once
const mockService = jasmine.createSpyObj('UserService', ['getUser', 'saveUser']);

This built-in spy support is Jasmine's equivalent of what Sinon.js provides for Mocha — no separate mocking library required.

Mocking Time

beforeEach(() => jasmine.clock().install());
afterEach(() => jasmine.clock().uninstall());

it('calls the callback after 5 seconds', () => {
  const callback = jasmine.createSpy();
  setTimeout(callback, 5000);
  jasmine.clock().tick(5001);   // instantly "fast-forward", no real waiting
  expect(callback).toHaveBeenCalled();
});

Async Matchers

it('resolves with the user', async () => {
  await expectAsync(fetchUser(1)).toBeResolvedTo({ id: 1, name: 'Ada' });
});

Jasmine + Karma, and the Jest Connection

Jasmine is the testing framework (structure, assertions, spies); Karma is a separate test runner that launches real browsers and executes the Jasmine specs in them — Angular's CLI historically defaulted to this pairing. Jest's syntax was heavily inspired by Jasmine's describe/it/expect pattern, adding a built-in runner, coverage, and snapshot testing on top.