describe, it, Matchers & Setup/Teardown

Batteries Included

Unlike Mocha (no built-in assertions, usually paired with Chai), Jasmine bundles test structure, assertions (expect), and mocking (spies) in one package — no separate library needed.

describe('UserService', () => {
  let service;

  beforeEach(() => {
    service = new UserService();
  });

  describe('login', () => {
    it('returns a token for valid credentials', () => {
      const result = service.login('ada', 'secret');
      expect(result.token).toBeTruthy();
    });
  });
});

describe() groups related specs under a label; it() defines one spec. beforeEach()/afterEach() run before/after every spec in the enclosing describe(); beforeAll()/afterAll() run exactly once for the whole suite.

toBe vs. toEqual

const a = { id: 1 };
const b = { id: 1 };

expect(a).toBe(a);       // passes — same reference
expect(a).toBe(b);       // FAILS — different instances
expect(a).toEqual(b);    // passes — deep comparison

expect(true).toBe(true);      // strict boolean check
expect(1).toBeTruthy();       // merely truthy — passes for 1, "x", {}
expect([1,2,3]).toContain(2);
expect(() => risky()).toThrow();  // pass a function reference, not a call

Focusing & Skipping

xit('skipped for now', () => { ... });     // x prefix skips
fit('only this runs', () => { ... });      // f prefix focuses