testing-strategies

name	testing-strategies
description	Comprehensive Angular testing strategies, patterns, and best practices for unit, integration, and E2E testing

Angular Testing Strategies

Comprehensive guide to testing strategies, patterns, and best practices for Angular applications.

Table of Contents

1. Testing Pyramid
2. Unit Testing Strategies
3. Integration Testing
4. E2E Testing
5. Test Organization
6. AAA Pattern
7. Test Doubles
8. Common Anti-Patterns
9. Performance Optimization
10. CI/CD Integration

---

Testing Pyramid

The ideal test distribution for Angular applications:

         ╱╲
        ╱ E2E ╲       (5% - Critical user journeys)
       ╱────────╲
      ╱Integration╲   (15% - Component + Service)
     ╱──────────────╲
    ╱   Unit Tests   ╲ (80% - Pure logic, services)
   ╱──────────────────╲

Why This Distribution?

• Unit Tests (80%): Fast, isolated, easy to maintain
• Integration Tests (15%): Test component interactions
• E2E Tests (5%): Slow but verify complete user flows

Cost vs Coverage

Test Type	Speed	Cost	Confidence	Maintenance
Unit	⚡⚡⚡	💰	⭐⭐	✅ Easy
Integration	⚡⚡	💰💰	⭐⭐⭐	⚠️ Medium
E2E	⚡	💰💰💰	⭐⭐⭐⭐	❌ Hard

---

Unit Testing Strategies

What to Unit Test

✅ DO Test:

• Pure functions and business logic
• Service methods
• Component methods (isolated)
• Pipes and custom validators
• Utility functions
• State management (reducers, selectors)

❌ DON'T Test:

• Angular framework internals
• Third-party libraries
• Simple getters/setters
• Generated code

Component Testing Approaches

1. Shallow Testing (Isolated)

Test component logic without rendering:

describe('UserProfileComponent (Shallow)', () => {
  let component: UserProfileComponent;
  let userService: jasmine.SpyObj<UserService>;

  beforeEach(() => {
    userService = jasmine.createSpyObj('UserService', ['getUser', 'updateUser']);
    component = new UserProfileComponent(userService);
  });

  it('should call updateUser with correct data', () => {
    const userData = { name: 'John', email: '[e-mail]' };
    userService.updateUser.and.returnValue(of({ success: true }));

    component.saveProfile(userData);

    expect(userService.updateUser).toHaveBeenCalledWith(userData);
  });
});

Pros: Fast, focused on logic
Cons: Doesn't test template integration
Use for: Complex business logic, services

2. Deep Testing (TestBed)

Test component with template and dependencies:

describe('UserProfileComponent (Deep)', () => {
  let component: UserProfileComponent;
  let fixture: ComponentFixture<UserProfileComponent>;
  let userService: jasmine.SpyObj<UserService>;

  beforeEach(async () => {
    const spy = jasmine.createSpyObj('UserService', ['getUser', 'updateUser']);

    await TestBed.configureTestingModule({
      declarations: [ UserProfileComponent ],
      imports: [ ReactiveFormsModule, HttpClientTestingModule ],
      providers: [
        { provide: UserService, useValue: spy }
      ]
    }).compileComponents();

    userService = TestBed.inject(UserService) as jasmine.SpyObj<UserService>;
    fixture = TestBed.createComponent(UserProfileComponent);
    component = fixture.componentInstance;
  });

  it('should display user name in template', () => {
    const userData = { name: 'John Doe', email: '[e-mail]' };
    userService.getUser.and.returnValue(of(userData));
    
    fixture.detectChanges(); // Trigger change detection

    const compiled = fixture.nativeElement;
    const nameElement = compiled.querySelector('.user-name');
    expect(nameElement.textContent).toContain('John Doe');
  });
});

Pros: Tests template + logic integration
Cons: Slower, more complex setup
Use for: UI interactions, template binding

Service Testing Patterns

Simple Service (No HTTP)

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

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

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

  it('should throw error for division by zero', () => {
    expect(() => service.divide(10, 0)).toThrow();
  });
});

HTTP Service Testing

describe('UserApiService', () => {
  let service: UserApiService;
  let httpMock: HttpTestingController;

  beforeEach(() => {
    TestBed.configureTestingModule({
      imports: [HttpClientTestingModule],
      providers: [UserApiService]
    });

    service = TestBed.inject(UserApiService);
    httpMock = TestBed.inject(HttpTestingController);
  });

  afterEach(() => {
    httpMock.verify(); // Ensure no outstanding requests
  });

  it('should fetch users', () => {
    const mockUsers = [
      { id: 1, name: 'John' },
      { id: 2, name: 'Jane' }
    ];

    service.getUsers().subscribe(users => {
      expect(users).toEqual(mockUsers);
    });

    const req = httpMock.expectOne('/api/users');
    expect(req.request.method).toBe('GET');
    req.flush(mockUsers);
  });

  it('should handle HTTP errors', () => {
    service.getUsers().subscribe({
      next: () => fail('should have failed'),
      error: (error) => {
        expect(error.status).toBe(500);
        expect(error.statusText).toBe('Server Error');
      }
    });

    const req = httpMock.expectOne('/api/users');
    req.flush('Error', { status: 500, statusText: 'Server Error' });
  });
});

Service with Dependencies

describe('AuthService', () => {
  let service: AuthService;
  let http: jasmine.SpyObj<HttpClient>;
  let router: jasmine.SpyObj<Router>;

  beforeEach(() => {
    const httpSpy = jasmine.createSpyObj('HttpClient', ['post', 'get']);
    const routerSpy = jasmine.createSpyObj('Router', ['navigate']);

    TestBed.configureTestingModule({
      providers: [
        AuthService,
        { provide: HttpClient, useValue: httpSpy },
        { provide: Router, useValue: routerSpy }
      ]
    });

    service = TestBed.inject(AuthService);
    http = TestBed.inject(HttpClient) as jasmine.SpyObj<HttpClient>;
    router = TestBed.inject(Router) as jasmine.SpyObj<Router>;
  });

  it('should login and navigate to dashboard', (done) => {
    const mockResponse = { token: 'fake-token' };
    http.post.and.returnValue(of(mockResponse));

    service.login('[e-mail]', 'password').subscribe(() => {
      expect(http.post).toHaveBeenCalledWith(
        '/api/auth/login',
        { email: '[e-mail]', password: 'password' }
      );
      expect(router.navigate).toHaveBeenCalledWith(['/dashboard']);
      done();
    });
  });
});

Pipe Testing

describe('FilterPipe', () => {
  let pipe: FilterPipe;

  beforeEach(() => {
    pipe = new FilterPipe();
  });

  it('should filter array by search term', () => {
    const items = [
      { name: 'Apple' },
      { name: 'Banana' },
      { name: 'Orange' }
    ];

    const result = pipe.transform(items, 'app', 'name');
    expect(result.length).toBe(1);
    expect(result[0].name).toBe('Apple');
  });

  it('should return empty array when no matches', () => {
    const items = [{ name: 'Apple' }];
    const result = pipe.transform(items, 'xyz', 'name');
    expect(result.length).toBe(0);
  });

  it('should return original array when search is empty', () => {
    const items = [{ name: 'Apple' }, { name: 'Banana' }];
    const result = pipe.transform(items, '', 'name');
    expect(result).toEqual(items);
  });
});

Directive Testing

describe('HighlightDirective', () => {
  let fixture: ComponentFixture<TestComponent>;
  let element: DebugElement;

  @Component({
    template: '<div appHighlight="yellow">Test</div>'
  })
  class TestComponent {}

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

    fixture = TestBed.createComponent(TestComponent);
    element = fixture.debugElement.query(By.directive(HighlightDirective));
    fixture.detectChanges();
  });

  it('should apply background color', () => {
    const bgColor = element.nativeElement.style.backgroundColor;
    expect(bgColor).toBe('yellow');
  });

  it('should change color on hover', () => {
    element.nativeElement.dispatchEvent(new MouseEvent('mouseenter'));
    fixture.detectChanges();
    expect(element.nativeElement.style.backgroundColor).toBe('orange');
  });
});

---

Integration Testing

Component + Service Integration

describe('ProductListComponent Integration', () => {
  let component: ProductListComponent;
  let fixture: ComponentFixture<ProductListComponent>;
  let productService: ProductService;
  let httpMock: HttpTestingController;

  beforeEach(async () => {
    await TestBed.configureTestingModule({
      declarations: [ ProductListComponent ],
      imports: [ HttpClientTestingModule, CommonModule ],
      providers: [ ProductService ]
    }).compileComponents();

    fixture = TestBed.createComponent(ProductListComponent);
    component = fixture.componentInstance;
    productService = TestBed.inject(ProductService);
    httpMock = TestBed.inject(HttpTestingController);
  });

  afterEach(() => {
    httpMock.verify();
  });

  it('should load and display products', () => {
    const mockProducts = [
      { id: 1, name: 'Product 1', price: 100 },
      { id: 2, name: 'Product 2', price: 200 }
    ];

    fixture.detectChanges(); // Trigger ngOnInit

    const req = httpMock.expectOne('/api/products');
    req.flush(mockProducts);
    fixture.detectChanges();

    const compiled = fixture.nativeElement;
    const productElements = compiled.querySelectorAll('.product-item');
    expect(productElements.length).toBe(2);
    expect(productElements[0].textContent).toContain('Product 1');
  });

  it('should handle loading state', () => {
    expect(component.isLoading).toBeFalsy();

    fixture.detectChanges(); // Trigger ngOnInit

    expect(component.isLoading).toBeTruthy();

    const req = httpMock.expectOne('/api/products');
    req.flush([]);

    expect(component.isLoading).toBeFalsy();
  });
});

Router + Guard Integration

describe('AuthGuard Integration', () => {
  let guard: AuthGuard;
  let authService: jasmine.SpyObj<AuthService>;
  let router: Router;
  let location: Location;

  beforeEach(async () => {
    const authServiceSpy = jasmine.createSpyObj('AuthService', ['isAuthenticated']);

    await TestBed.configureTestingModule({
      imports: [RouterTestingModule.withRoutes([
        { path: 'dashboard', component: DummyComponent, canActivate: [AuthGuard] },
        { path: 'login', component: DummyComponent }
      ])],
      providers: [
        AuthGuard,
        { provide: AuthService, useValue: authServiceSpy }
      ]
    }).compileComponents();

    guard = TestBed.inject(AuthGuard);
    authService = TestBed.inject(AuthService) as jasmine.SpyObj<AuthService>;
    router = TestBed.inject(Router);
    location = TestBed.inject(Location);
  });

  it('should allow navigation when authenticated', fakeAsync(() => {
    authService.isAuthenticated.and.returnValue(true);

    router.navigate(['/dashboard']);
    tick();

    expect(location.path()).toBe('/dashboard');
  }));

  it('should redirect to login when not authenticated', fakeAsync(() => {
    authService.isAuthenticated.and.returnValue(false);

    router.navigate(['/dashboard']);
    tick();

    expect(location.path()).toBe('/login');
  }));
});

---

E2E Testing

Cypress E2E Strategy

// cypress/e2e/user-journey.cy.ts
describe('Complete User Journey', () => {
  beforeEach(() => {
    // Reset database state
    cy.task('db:seed');
    cy.visit('/');
  });

  it('should complete purchase flow', () => {
    // Login
    cy.getBySel('login-button').click();
    cy.getBySel('email-input').type('[e-mail]');
    cy.getBySel('password-input').type('password123');
    cy.getBySel('submit-button').click();

    // Browse products
    cy.url().should('include', '/products');
    cy.getBySel('product-card').first().click();

    // Add to cart
    cy.getBySel('add-to-cart-button').click();
    cy.getBySel('cart-badge').should('contain', '1');

    // Checkout
    cy.getBySel('cart-icon').click();
    cy.getBySel('checkout-button').click();

    // Fill shipping info
    cy.getBySel('address-input').type('123 Main St');
    cy.getBySel('city-input').type('New York');
    cy.getBySel('zipcode-input').type('10001');

    // Complete purchase
    cy.getBySel('complete-order-button').click();
    cy.url().should('include', '/order-confirmation');
    cy.getBySel('success-message').should('be.visible');
  });
});

Playwright E2E Strategy

// e2e/user-journey.spec.ts
import { test, expect } from '@playwright/test';

test.describe('Complete User Journey', () => {
  test.beforeEach(async ({ page }) => {
    await page.goto('/');
  });

  test('should complete purchase flow', async ({ page }) => {
    // Login
    await page.click('[data-testid="login-button"]');
    await page.fill('[data-testid="email-input"]', '[e-mail]');
    await page.fill('[data-testid="password-input"]', 'password123');
    await page.click('[data-testid="submit-button"]');

    // Wait for navigation
    await page.waitForURL('**/products');

    // Browse products
    await page.click('[data-testid="product-card"] >> nth=0');

    // Add to cart
    await page.click('[data-testid="add-to-cart-button"]');
    await expect(page.locator('[data-testid="cart-badge"]')).toHaveText('1');

    // Checkout
    await page.click('[data-testid="cart-icon"]');
    await page.click('[data-testid="checkout-button"]');

    // Fill shipping info
    await page.fill('[data-testid="address-input"]', '123 Main St');
    await page.fill('[data-testid="city-input"]', 'New York');
    await page.fill('[data-testid="zipcode-input"]', '10001');

    // Complete purchase
    await page.click('[data-testid="complete-order-button"]');
    await expect(page).toHaveURL(/.*order-confirmation/);
    await expect(page.locator('[data-testid="success-message"]')).toBeVisible();
  });
});

---

Test Organization

File Structure

src/app/
├── components/
│   ├── user-profile/
│   │   ├── user-profile.component.ts
│   │   ├── user-profile.component.spec.ts
│   │   ├── user-profile.component.html
│   │   └── user-profile.component.scss
│   └── shared/
│       └── button/
│           ├── button.component.ts
│           └── button.component.spec.ts
├── services/
│   ├── auth.service.ts
│   ├── auth.service.spec.ts
│   ├── user.service.ts
│   └── user.service.spec.ts
├── guards/
│   ├── auth.guard.ts
│   └── auth.guard.spec.ts
├── pipes/
│   ├── filter.pipe.ts
│   └── filter.pipe.spec.ts
└── testing/
    ├── mocks/
    │   ├── mock-auth.service.ts
    │   └── mock-user.service.ts
    ├── fixtures/
    │   ├── user.fixture.ts
    │   └── product.fixture.ts
    └── helpers/
        ├── test-utils.ts
        └── custom-matchers.ts

Test Helper Functions

// src/app/testing/helpers/test-utils.ts

/**
 * Create a mock Observable that emits immediately
 */
export function createMockObservable<T>(data: T): Observable<T> {
  return of(data);
}

/**
 * Create a mock Observable that throws an error
 */
export function createMockError(error: any): Observable<never> {
  return throwError(() => error);
}

/**
 * Click a button and wait for async operations
 */
export async function clickButton(
  fixture: ComponentFixture<any>,
  selector: string
): Promise<void> {
  const button = fixture.nativeElement.querySelector(selector);
  button.click();
  fixture.detectChanges();
  await fixture.whenStable();
}

/**
 * Set form values
 */
export function setFormValues(
  form: FormGroup,
  values: { [key: string]: any }
): void {
  Object.keys(values).forEach(key => {
    const control = form.get(key);
    if (control) {
      control.setValue(values[key]);
      control.markAsTouched();
    }
  });
}

/**
 * Create spy object with typed methods
 */
export function createSpyObj<T>(
  baseName: string,
  methodNames: (keyof T)[]
): jasmine.SpyObj<T> {
  return jasmine.createSpyObj(baseName, methodNames as string[]);
}

Test Fixtures

// src/app/testing/fixtures/user.fixture.ts

export class UserFixtures {
  static readonly VALID_USER = {
    id: 1,
    email: '[e-mail]',
    name: 'Test User',
    role: 'user'
  };

  static readonly ADMIN_USER = {
    id: 2,
    email: '[e-mail]',
    name: 'Admin User',
    role: 'admin'
  };

  static readonly USER_LIST = [
    UserFixtures.VALID_USER,
    UserFixtures.ADMIN_USER,
    {
      id: 3,
      email: '[e-mail]',
      name: 'User Three',
      role: 'user'
    }
  ];

  static createUser(overrides: Partial<User> = {}): User {
    return {
      ...UserFixtures.VALID_USER,
      ...overrides
    };
  }
}

---

AAA Pattern

Arrange-Act-Assert Structure

describe('ShoppingCartService', () => {
  it('should add item to cart', () => {
    // ===== ARRANGE =====
    // Set up test data and dependencies
    const service = new ShoppingCartService();
    const product = {
      id: 1,
      name: 'Test Product',
      price: 99.99
    };

    // ===== ACT =====
    // Execute the behavior being tested
    service.addToCart(product);

    // ===== ASSERT =====
    // Verify the expected outcome
    expect(service.getCartItems().length).toBe(1);
    expect(service.getCartItems()[0]).toEqual(product);
    expect(service.getTotal()).toBe(99.99);
  });
});

Why AAA Pattern?

✅ Readability: Clear test structure
✅ Maintainability: Easy to update
✅ Debugging: Quickly identify failures
✅ Consistency: Uniform test style

Common Variations

// Given-When-Then (BDD style)
it('should add item to cart', () => {
  // GIVEN: A shopping cart and a product
  const service = new ShoppingCartService();
  const product = { id: 1, name: 'Product', price: 99.99 };

  // WHEN: Adding the product to cart
  service.addToCart(product);

  // THEN: Cart should contain the product
  expect(service.getCartItems()).toContain(product);
});

---

Test Doubles

Types of Test Doubles

1. Dummy: Passed but never used
2. Stub: Provides preset responses
3. Spy: Records how it was called
4. Mock: Pre-programmed with expectations
5. Fake: Working implementation (simplified)

Jasmine Spies

// Creating spies
const spy = jasmine.createSpy('myFunction');
const spyObj = jasmine.createSpyObj('MyService', ['method1', 'method2']);

// Spy on existing method
spyOn(service, 'getData').and.returnValue(of(mockData));

// Spy configurations
spy.and.returnValue(42);
spy.and.returnValues(1, 2, 3);
spy.and.callFake(() => 'custom logic');
spy.and.callThrough(); // Call actual method
spy.and.throwError('error message');

// Assertions
expect(spy).toHaveBeenCalled();
expect(spy).toHaveBeenCalledTimes(2);
expect(spy).toHaveBeenCalledWith('arg1', 'arg2');
expect(spy).toHaveBeenCalledBefore(anotherSpy);

Mock HTTP Responses

it('should handle successful API call', () => {
  service.getUsers().subscribe(users => {
    expect(users.length).toBe(2);
  });

  const req = httpMock.expectOne('/api/users');
  expect(req.request.method).toBe('GET');
  
  req.flush([
    { id: 1, name: 'User 1' },
    { id: 2, name: 'User 2' }
  ]);
});

it('should handle API errors', () => {
  service.getUsers().subscribe({
    error: (error) => {
      expect(error.status).toBe(404);
    }
  });

  const req = httpMock.expectOne('/api/users');
  req.flush('Not Found', { status: 404, statusText: 'Not Found' });
});

---

Common Anti-Patterns

❌ Testing Implementation Details

// BAD: Testing private methods
it('should call private method', () => {
  spyOn(component as any, 'privateMethod');
  component.publicMethod();
  expect((component as any).privateMethod).toHaveBeenCalled();
});

// GOOD: Test public behavior
it('should update user list', () => {
  component.refreshUsers();
  expect(component.users.length).toBeGreaterThan(0);
});

❌ Flaky Tests

// BAD: Time-dependent tests
it('should update after delay', (done) => {
  service.delayedUpdate();
  setTimeout(() => {
    expect(service.value).toBe(42);
    done();
  }, 100); // Magic number!
});

// GOOD: Use fakeAsync
it('should update after delay', fakeAsync(() => {
  service.delayedUpdate();
  tick(1000);
  expect(service.value).toBe(42);
}));

❌ Test Interdependence

// BAD: Tests depend on each other
describe('UserService', () => {
  let userId: number;

  it('should create user', () => {
    userId = service.createUser({ name: 'Test' });
    expect(userId).toBeDefined();
  });

  it('should get user', () => {
    const user = service.getUser(userId); // Depends on previous test!
    expect(user.name).toBe('Test');
  });
});

// GOOD: Independent tests
describe('UserService', () => {
  beforeEach(() => {
    // Reset state before each test
    service.clear();
  });

  it('should create user', () => {
    const userId = service.createUser({ name: 'Test' });
    expect(userId).toBeDefined();
  });

  it('should get user', () => {
    const userId = service.createUser({ name: 'Test' });
    const user = service.getUser(userId);
    expect(user.name).toBe('Test');
  });
});

❌ Over-Mocking

// BAD: Mocking everything
it('should calculate total', () => {
  spyOn(Math, 'round').and.returnValue(100);
  spyOn(Math, 'floor').and.returnValue(99);
  // Too many mocks!
});

// GOOD: Only mock external dependencies
it('should calculate total', () => {
  const cart = new ShoppingCart();
  cart.addItem({ price: 10, quantity: 3 });
  expect(cart.getTotal()).toBe(30);
});

---

Performance Optimization

Run Tests in Parallel

// karma.conf.js
module.exports = function(config) {
  config.set({
    browsers: ['ChromeHeadless'],
    concurrency: 5, // Run 5 instances in parallel
    browserNoActivityTimeout: 60000
  });
};

Use Shallow Testing When Possible

// Fast: Shallow test
describe('Component (Shallow)', () => {
  it('should calculate total', () => {
    const component = new PriceCalculatorComponent();
    component.price = 100;
    component.quantity = 2;
    expect(component.total).toBe(200);
  });
});

// Slow: Full TestBed
describe('Component (Deep)', () => {
  let fixture: ComponentFixture<PriceCalculatorComponent>;
  
  beforeEach(async () => {
    await TestBed.configureTestingModule({
      declarations: [ PriceCalculatorComponent ],
      imports: [ CommonModule, FormsModule ]
    }).compileComponents();
    
    fixture = TestBed.createComponent(PriceCalculatorComponent);
  });

  it('should calculate total', () => {
    // Much slower setup
  });
});

Skip Heavy Tests in Watch Mode

// Use fdescribe/fit for focused testing during development
fdescribe('UserComponent', () => {
  fit('should create', () => {
    expect(component).toBeTruthy();
  });
});

// Or use xdescribe/xit to skip tests
xdescribe('SlowE2ETests', () => {
  // These tests won't run
});

---

CI/CD Integration

GitHub Actions

name: Tests

on: [push, pull_request]

jobs:
  test:
    runs-on: ubuntu-latest
    
    steps:
      - uses: actions/checkout@v3
      
      - uses: actions/setup-node@v3
        with:
          node-version: '20'
          cache: 'npm'
      
      - name: Install dependencies
        run: npm ci
      
      - name: Run unit tests
        run: npm run test:ci
      
      - name: Generate coverage
        run: npm run test:coverage
      
      - name: Upload coverage to Codecov
        uses: codecov/codecov-action@v3
        with:
          files: ./coverage/lcov.info
      
      - name: Run E2E tests
        run: npm run e2e:ci
      
      - name: Upload test results
        if: always()
        uses: actions/upload-artifact@v3
        with:
          name: test-results
          path: |
            coverage/
            cypress/screenshots/
            cypress/videos/

Package.json Scripts

{
  "scripts": {
    "test": "ng test",
    "test:ci": "ng test --watch=false --browsers=ChromeHeadless --code-coverage",
    "test:coverage": "ng test --code-coverage --watch=false",
    "test:watch": "ng test --watch=true",
    "e2e": "cypress open",
    "e2e:ci": "cypress run --browser chrome"
  }
}

---

Best Practices Summary

✅ DO:

• Follow AAA pattern
• Test behavior, not implementation
• Keep tests isolated and independent
• Use descriptive test names
• Mock external dependencies
• Aim for 80% code coverage
• Run tests before committing
• Use CI/CD for automated testing

❌ DON'T:

• Test framework internals
• Create dependent tests
• Use magic numbers or strings
• Test private methods
• Ignore flaky tests
• Skip edge cases
• Over-mock everything

---

Quick Reference

Test Types

Type	Purpose	Speed	Coverage
Unit	Test isolated logic	⚡⚡⚡	80%
Integration	Test component + service	⚡⚡	15%
E2E	Test user workflows	⚡	5%

Common Matchers

expect(value).toBe(42);
expect(value).toEqual({ id: 1 });
expect(value).toBeTruthy();
expect(value).toBeFalsy();
expect(array).toContain(item);
expect(fn).toThrow();
expect(spy).toHaveBeenCalled();
expect(spy).toHaveBeenCalledWith(arg);

Async Testing

// Using done()
it('async test', (done) => {
  service.getData().subscribe(data => {
    expect(data).toBeTruthy();
    done();
  });
});

// Using fakeAsync
it('async test', fakeAsync(() => {
  service.delayedAction();
  tick(1000);
  expect(service.value).toBe(42);
}));

// Using async/await
it('async test', async () => {
  const data = await service.getData().toPromise();
  expect(data).toBeTruthy();
});

---

Master these strategies to build bulletproof Angular applications! 🛡️