Testing with fixtures and debug elements in Angular - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the rendered output of this Angular test fixture?

Given the following Angular component and test setup, what will be the text content of the

element accessed via debugElement.nativeElement?

Angular

import { Component } from '@angular/core';
import { ComponentFixture, TestBed } from '@angular/core/testing';
import { By } from '@angular/platform-browser';

@Component({
  selector: 'app-greet',
  template: `<p>Hello, {{name}}!</p>`
})
class GreetComponent {
  name = 'Alice';
}

// Test setup
let fixture: ComponentFixture<GreetComponent>;

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

const pElement = fixture.debugElement.query(By.css('p')).nativeElement;
const textContent = pElement.textContent.trim();

A "Hello, Alice!"

B "Hello, !"

C "{{name}}"

D "Hello, undefined!"

💡 Hint

Remember that fixture.detectChanges() triggers Angular's change detection to update the template bindings.

The component initializes name as 'Alice'. After fixture.detectChanges(), Angular updates the template, so the <p> element shows "Hello, Alice!".

🔧 Debug

intermediate

Which debugElement query will select the button with class 'submit-btn'?

In an Angular test, you want to select a button element with the class 'submit-btn' using the fixture's debugElement. Which of the following queries will correctly select it?

A fixture.debugElement.query(By.directive('submit-btn'))

B fixture.debugElement.query(By.css('button.submit-btn'))

C fixture.debugElement.query(By.css('.submit-btn button'))

D fixture.debugElement.query(By.css('button#submit-btn'))

💡 Hint

Use CSS selectors to target elements by tag and class.

The selector button.submit-btn matches a <button> element with class submit-btn. The other options either misuse directive selectors or incorrect CSS selectors.

📝 Syntax

advanced

What error does this Angular test code produce?

Consider this Angular test snippet: const button = fixture.debugElement.query(By.css('button')); button.nativeElement.click(); fixture.detectChanges(); What error will occur if the button element is not present in the component template?

A ReferenceError: fixture is not defined

B No error, test passes silently

C SyntaxError: Unexpected token '.'

D TypeError: Cannot read property 'click' of null

💡 Hint

What happens if query returns null and you try to access nativeElement?

If query returns null because the element is missing, then button is null. Accessing button.nativeElement causes a TypeError.

❓ state_output

advanced

What is the value of 'count' after this test code runs?

Given this Angular component and test code: @Component({ template: `

{{count}}

` }) class CounterComponent { count = 0; increment() { this.count++; } } // Test const fixture = TestBed.createComponent(CounterComponent); fixture.detectChanges(); const button = fixture.debugElement.query(By.css('button')); button.triggerEventHandler('click', null); fixture.detectChanges(); const displayedCount = fixture.componentInstance.count;

A undefined

B 0

C 1

D NaN

💡 Hint

Triggering the click event calls increment which increases count.

The increment() method increases count by 1 when the button is clicked. After triggering the click and running change detection, count is 1.

🧠 Conceptual

expert

Why use fixture.debugElement instead of nativeElement in Angular tests?

Which of the following is the best reason to prefer using fixture.debugElement over fixture.nativeElement when querying elements in Angular tests?

A debugElement provides Angular-specific utilities like querying by directive and event triggering, which nativeElement lacks

B debugElement automatically triggers change detection after every query

C nativeElement is deprecated and will be removed in future Angular versions

D nativeElement only works with server-side rendering and not in browser tests

💡 Hint

Think about what extra features debugElement offers beyond raw DOM access.

debugElement wraps native DOM elements and adds Angular-specific methods like querying by directives, triggering event handlers, and accessing component instances. nativeElement is just the raw DOM node without these features.