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Frontend Angular Testing Performance Interview Questions

75 verified Frontend Angular Testing Performance interview questions — solve with answers, learn from explanations, test yourself in a real simulation.

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Sample questions

Angular Testing PerformanceDifficulty 1
In an Angular unit test, what is the main purpose of TestBed.configureTestingModule({...})?
  • aTo start the production build process for the application
  • bTo set up an Angular testing module with the declarations/imports/providers a test needs✓
  • cTo open a real browser window and run end-to-end tests
  • dTo bundle the application, minify its output, and measure the final production bundle size after building
Explanation:TestBed.configureTestingModule() creates a dedicated Angular module scoped to the test, letting you declare the component under test and supply the imports/providers it depends on. It's the standard entry point for Angular unit tests written with Jasmine/Karma.
Angular Testing PerformanceDifficulty 1
let fixture: ComponentFixture<CounterComponent>;

beforeEach(() => {
  TestBed.configureTestingModule({ declarations: [CounterComponent] });
  fixture = TestBed.createComponent(CounterComponent);
});

After fixture.detectChanges() is called for the first time, what happens?
  • aThe component is destroyed and ngOnDestroy runs
  • bNothing, detectChanges() only works after ngOnInit has already fired
  • cAngular runs change detection, which also triggers ngOnInit on first call✓
  • dThe component's template is compiled for the very first time
Explanation:In tests, Angular does not run change detection automatically. Calling fixture.detectChanges() triggers the component's lifecycle (including the initial ngOnInit) and updates the rendered DOM to match the current component state.
Angular Testing PerformanceDifficulty 2
In a classic Karma-based Angular unit-test setup, which tools play the framework and browser-runner roles?
  • aJasmine as the test framework, Karma as the test runner✓
  • bMocha as the test framework, Cypress as the test runner
  • cJest as the test framework, Playwright as the test runner
  • dJUnit as the test framework, Selenium as the test runner
Explanation:In this setup, Jasmine supplies the describe/it/expect test API and Karma launches browsers and runs the specs. Angular CLI defaults have changed across versions, so the pairing should be identified by the configured runner rather than assumed to be every new project's current default.
Angular Testing PerformanceDifficulty 1
class MathService {
  square(n: number): number {
    return n * n;
  }
}

describe('MathService', () => {
  it('squares a number', () => {
    const service = new MathService();
    expect(service.square(4)).toBe(16);
  });
});

Why can this service test skip TestBed entirely?
  • aJasmine tests never need TestBed, regardless of the class under test
  • bMathService uses @Injectable, so Angular provides it automatically
  • cTestBed only works for components, never for services
  • dMathService has no dependencies, so it can be instantiated directly with new✓
Explanation:TestBed matters when Angular's dependency injection needs to resolve constructor dependencies or when a component needs a rendering environment. A plain class with no injected dependencies can simply be instantiated with new, keeping the test fast and simple.
Angular Testing PerformanceDifficulty 2
it('renders the title', () => {
  fixture.detectChanges();
  const el: HTMLElement = fixture.nativeElement;
  expect(el.querySelector('h1')?.textContent).toContain('Dashboard');
});

What does fixture.nativeElement give access to?
  • aThe TypeScript class instance of the component
  • bThe root DOM element rendered by the component✓
  • cThe Angular module the component was declared in
  • dA mock version of the DOM that never actually renders
Explanation:fixture.nativeElement exposes the actual rendered DOM node for the component's host element, so tests can query it with standard DOM APIs like querySelector to assert on rendered content. The component instance itself is available separately via fixture.componentInstance.
Angular Testing PerformanceDifficulty 2
What is fakeAsync primarily used for in Angular tests?
  • aTo run asynchronous code (timers, promises) in a synchronous-looking test zone that can be controlled with tick()✓
  • bTo automatically mock every HTTP call made during the test
  • cIt automatically retries every HTTP call made anywhere during the test, regardless of endpoint or status code
  • dTo make a real network request faster by caching the response
Explanation:fakeAsync wraps a test function in a special zone where asynchronous operations like setTimeout and promise resolution can be simulated and advanced deterministically using tick(), instead of relying on real elapsed time.

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