Jasmine Testing Skill

Core Patterns

Basic Test

describe('Calculator', () => {
  let calc;

  beforeEach(() => { calc = new Calculator(); });

  it('should add two numbers', () => {
    expect(calc.add(2, 3)).toBe(5);
  });

  it('should throw on divide by zero', () => {
    expect(() => calc.divide(10, 0)).toThrowError('Division by zero');
  });
});

Matchers

expect(value).toBe(exact);              // === strict
expect(value).toEqual(object);           // Deep equality
expect(value).toBeTruthy();
expect(value).toBeFalsy();
expect(value).toBeNull();
expect(value).toBeUndefined();
expect(value).toBeDefined();
expect(value).toBeNaN();
expect(value).toBeGreaterThan(3);
expect(value).toBeCloseTo(0.3, 5);
expect(str).toContain('sub');
expect(str).toMatch(/pattern/);
expect(arr).toContain(item);
expect(fn).toThrow();
expect(fn).toThrowError('message');

// Negation
expect(value).not.toBe(other);

Spies

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

  beforeEach(() => {
    api = jasmine.createSpyObj('api', ['get', 'post']);
    service = new UserService(api);
  });

  it('fetches user from API', async () => {
    api.get.and.returnValue(Promise.resolve({ name: 'Alice' }));
    const user = await service.getUser(1);
    expect(user.name).toBe('Alice');
    expect(api.get).toHaveBeenCalledWith('/users/1');
    expect(api.get).toHaveBeenCalledTimes(1);
  });
});

// Spy on existing method
spyOn(obj, 'method').and.returnValue(42);
spyOn(obj, 'method').and.callThrough();    // Call original
spyOn(obj, 'method').and.throwError('err');

Async Testing

it('fetches data', async () => {
  const data = await fetchData();
  expect(data).toBeDefined();
});

// With done callback
it('fetches data', (done) => {
  fetchData().then(data => {
    expect(data).toBeDefined();
    done();
  });
});

// Clock control
beforeEach(() => { jasmine.clock().install(); });
afterEach(() => { jasmine.clock().uninstall(); });

it('handles timeout', () => {
  const callback = jasmine.createSpy();
  setTimeout(callback, 1000);
  jasmine.clock().tick(1001);
  expect(callback).toHaveBeenCalled();
});

Setup: npm install jasmine --save-dev && npx jasmine init

Run: npx jasmine or npx jasmine spec/calculatorSpec.js

Deep Patterns

See reference/playbook.md for production-grade patterns: