#14 Testing and Debugging Angular Applications

#14 Testing and Debugging Angular Applications

Testing and debugging are crucial steps in the development process to ensure that your Angular applications are reliable, maintainable, and performant. This article provides an overview of testing and debugging in Angular, including unit testing with Jasmine and Karma, end-to-end testing with Protractor, debugging techniques, and performance optimization best practices.

10.1 Introduction to Testing

Testing helps ensure that your application behaves as expected and helps identify and fix bugs early in the development process. In Angular, testing can be broadly categorized into two types:

  • Unit Testing: Tests individual components, services, and other units of code to ensure they function correctly.
  • End-to-End (E2E) Testing: Tests the entire application flow to ensure that all parts work together as expected.

10.2 Unit Testing with Jasmine and Karma


Jasmine is a behavior-driven development framework for testing JavaScript code. It provides functions to write tests, group them into suites, and make assertions.


Karma is a test runner that runs your tests in different browsers, reporting the results back to you in real-time.

Setting Up Jasmine and Karma

Angular CLI sets up Jasmine and Karma for you when you create a new Angular project. To start testing, simply run:

ng test

Writing Unit Tests

Unit tests are written using Jasmine’s describe, it, and expect functions. Here’s an example of a simple unit test for an Angular service:

  • Create a Service:
import { Injectable } from '@angular/core';

  providedIn: 'root'
export class MathService {
  add(a: number, b: number): number {
    return a + b;

  • Write a Unit Test:
import { TestBed } from '@angular/core/testing';
import { MathService } from './math.service';

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

  beforeEach(() => {
    service = TestBed.inject(MathService);

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

Testing Components

To test components, you need to configure a testing module and compile the component.

import { ComponentFixture, TestBed } from '@angular/core/testing';
import { MyComponent } from './my-component.component';

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

  beforeEach(async () => {
    await TestBed.configureTestingModule({
      declarations: [ MyComponent ]

  beforeEach(() => {
    fixture = TestBed.createComponent(MyComponent);
    component = fixture.componentInstance;

  it('should create', () => {

10.3 End-to-End Testing with Protractor

Protractor is an end-to-end testing framework for Angular applications. It runs tests in a real browser, simulating user interactions.

Setting Up Protractor

Protractor is included when you create a new Angular project. To start E2E testing, run:

ng e2e

Writing E2E Tests

E2E tests are written using Jasmine syntax. Here’s an example of a simple E2E test:

  1. Sample Test:
import { browser, by, element } from 'protractor';

describe('workspace-project App', () => {
  it('should display welcome message', () => {
    expect(element(by.css('app-root h1')).getText()).toEqual('Welcome to app!');

10.4 Debugging Angular Applications

Debugging is essential to find and fix issues in your application. Angular provides several tools and techniques for effective debugging.

Using Angular DevTools

Angular DevTools is a browser extension that helps you inspect and debug Angular applications. It provides features like component tree inspection, performance profiling, and change detection debugging.

Debugging in Chrome DevTools

Chrome DevTools is a powerful tool for debugging JavaScript applications. You can set breakpoints, inspect variables, and view the call stack.

Using console.log

Using console.log is a simple yet effective way to debug your code by printing variable values and execution flow to the console.

Error Handling

Angular provides a global error handler to catch and handle errors across the application.

import { ErrorHandler, Injectable } from '@angular/core';

export class GlobalErrorHandler implements ErrorHandler {
  handleError(error: any): void {
    console.error('An error occurred:', error.message);

10.5 Performance Optimization and Best Practices

Performance optimization ensures that your Angular applications run efficiently and provide a smooth user experience. Here are some best practices:

Lazy Loading

Lazy loading modules can significantly reduce the initial load time by loading parts of the application only when needed.

OnPush Change Detection

Using OnPush change detection strategy can improve performance by reducing the number of change detection cycles.

import { ChangeDetectionStrategy, Component } from '@angular/core';

  selector: 'app-my-component',
  templateUrl: './my-component.component.html',
  changeDetection: ChangeDetectionStrategy.OnPush
export class MyComponent {}

AOT Compilation

Ahead-of-Time (AOT) compilation compiles your Angular application during the build process, resulting in faster rendering.

ng build --prod

TrackBy in *ngFor

Using trackBy in *ngFor helps Angular track items in lists more efficiently.

<div *ngFor="let item of items; trackBy: trackByFn">{{ item.name }}</div>
trackByFn(index, item) {
  return item.id; // or any unique identifier

Minification and Bundling

Minifying and bundling your JavaScript files can reduce the size of your application, leading to faster load times.

ng build --prod

Caching and Service Workers

Using service workers and caching strategies can improve the performance and offline capabilities of your application.

ng add @angular/pwa


Testing and debugging are vital for building high-quality Angular applications. By utilizing tools like Jasmine, Karma, Protractor, and Angular DevTools, you can ensure your application is reliable and performant. Following best practices for performance optimization will help you create fast, responsive, and efficient applications.


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