Angular Testing

ng test   # Runs all tests, watches for changes

export function calculateTotal(price: number, quantity: number): number {
  return price * quantity;
}

import { calculateTotal } from './math.utils';

describe('calculateTotal', () => {
  it('should multiply price by quantity', () => {
    expect(calculateTotal(10, 5)).toBe(50);
  });

  it('should return 0 for zero quantity', () => {
    expect(calculateTotal(100, 0)).toBe(0);
  });

  it('should handle decimal prices', () => {
    expect(calculateTotal(9.99, 3)).toBeCloseTo(29.97);
  });
});

import { TestBed } from '@angular/core/testing';
import { TaskService } from './task.service';

describe('TaskService', () => {
  let service: TaskService;

  beforeEach(() => {
    TestBed.configureTestingModule({});
    service = TestBed.inject(TaskService);
  });

  it('should be created', () => {
    expect(service).toBeTruthy();
  });

  it('should start with initial tasks', () => {
    const tasks = service.getTasks();
    expect(tasks.length).toBeGreaterThan(0);
  });

  it('should add a new task', () => {
    const initialCount = service.getTasks().length;
    service.addTask('New test task');
    expect(service.getTasks().length).toBe(initialCount + 1);
  });

  it('should delete a task by index', () => {
    service.addTask('Task to delete');
    const countBefore = service.getTasks().length;
    service.deleteTask(countBefore - 1);
    expect(service.getTasks().length).toBe(countBefore - 1);
  });
});

import { ComponentFixture, TestBed } from '@angular/core/testing';
import { CounterComponent } from './counter.component';

describe('CounterComponent', () => {
  let component: CounterComponent;
  let fixture: ComponentFixture<CounterComponent>;

  beforeEach(async () => {
    await TestBed.configureTestingModule({
      declarations: [CounterComponent]
    }).compileComponents();

    fixture = TestBed.createComponent(CounterComponent);
    component = fixture.componentInstance;
    fixture.detectChanges(); // Triggers ngOnInit
  });

  it(&#039;should create&#039;, () => {
    expect(component).toBeTruthy();
  });

  it(&#039;should display initial count of 0&#039;, () => {
    const h2: HTMLElement = fixture.nativeElement.querySelector(&#039;h2&#039;);
    expect(h2.textContent).toContain(&#039;0&#039;);
  });

  it(&#039;should increment count when button is clicked&#039;, () => {
    const button: HTMLButtonElement = fixture.nativeElement.querySelector(&#039;button&#039;);
    button.click();
    fixture.detectChanges(); // Update the view

    const h2: HTMLElement = fixture.nativeElement.querySelector(&#039;h2&#039;);
    expect(h2.textContent).toContain(&#039;1&#039;);
    expect(component.count).toBe(1);
  });
});

import { of } from 'rxjs';
import { UserService } from '../user.service';

describe('UserListComponent', () => {
  let mockUserService: jasmine.SpyObj<UserService>;

  beforeEach(async () => {
    mockUserService = jasmine.createSpyObj(&#039;UserService&#039;, [&#039;getUsers&#039;]);
    // Return fake data instead of real HTTP call
    mockUserService.getUsers.and.returnValue(of([
      { id: 1, name: &#039;Alice&#039; },
      { id: 2, name: &#039;Bob&#039; }
    ]));

    await TestBed.configureTestingModule({
      declarations: [UserListComponent],
      providers: [
        { provide: UserService, useValue: mockUserService } // Inject mock
      ]
    }).compileComponents();
  });

  it(&#039;should display 2 users&#039;, () => {
    fixture.detectChanges();
    const items = fixture.nativeElement.querySelectorAll(&#039;li&#039;);
    expect(items.length).toBe(2);
  });
});

expect(value).toBe(exact);           // Strict equality ===
expect(value).toEqual(deepEqual);    // Deep equality (objects, arrays)
expect(value).toBeTruthy();          // Not null, 0, '', false
expect(value).toBeFalsy();           // null, 0, '', false
expect(value).toBeNull();
expect(value).toBeUndefined();
expect(value).toContain('substring');
expect(arr).toContain(item);
expect(value).toBeGreaterThan(num);
expect(fn).toThrow();                // Function throws an error
expect(spy).toHaveBeenCalled();      // Spy was called
expect(spy).toHaveBeenCalledWith(arg); // Spy called with specific args