Angular Unit Testing with Jasmine and Karma Step by step Implementation and Top 10 Questions and Answers
 Last Update:6/1/2025 12:00:00 AM     .NET School AI Teacher - SELECT ANY TEXT TO EXPLANATION.    16 mins read      Difficulty-Level: beginner

Angular Unit Testing with Jasmine and Karma: An In-Depth Guide

Unit testing is a fundamental part of any software development process. It helps in ensuring that various components of the software work as intended. In the context of Angular, unit testing becomes even more critical due to its robust architecture and dynamic nature. Angular provides a powerful testing framework that utilizes Jasmine for writing test cases and Karma for executing these tests in a variety of environments.

1. Introduction to Jasmine:

Jasmine is a Behavior-Driven Development (BDD) style JavaScript testing framework. It doesn't rely on any other JavaScript frameworks, and it has a clean, intuitive syntax. With Jasmine, you can write focused tests to validate functions, components, and services.

2. Introduction to Karma:

Karma is a test runner that runs your tests across different browsers and platforms. It's lightweight, modular, and very easy to set up. Karma can automatically run tests on any changes you make to your code, making it an essential tool for continuous integration.

3. Setting Up Angular Testing:

Angular CLI makes setting up testing easy. When you generate a new Angular project or component, it automatically includes configuration files for Jasmine and Karma.

Key Configuration File:

  • karma.conf.js: This file is the main configuration file for Karma. It tells Karma which browsers to use, which files to load, and which test frameworks to use (in this case, Jasmine). Here’s an example snippet:
module.exports = function(config) {
  config.set({
    basePath: '',
    frameworks: ['jasmine', '@angular-devkit/build-angular'],
    plugins: [
      require('karma-jasmine'),
      require('karma-chrome-launcher'),
      require('karma-jasmine-html-reporter'),
      require('karma-coverage-istanbul-reporter'),
      require('@angular-devkit/build-angular/plugins/karma')
    ],
    client: {
      clearContext: false // leave Jasmine Spec Runner output visible in browser
    },
    coverageIstanbulReporter: {
      dir: require('path').join(__dirname, '../coverage'),
      reports: ['html', 'lcovonly'],
      fixWebpackSourcePaths: true
    },
    reporters: ['progress', 'kjhtml'],
    port: 9876,
    colors: true,
    logLevel: config.LOG_INFO,
    autoWatch: true,
    browsers: ['Chrome'],
    singleRun: false,
    restartOnFileChange: true
  });
};

4. Writing Unit Tests in Angular:

Writing unit tests in Angular involves using Jasmine’s syntax to define test cases. Here’s how you can write and structure your tests:

Example: Testing an Angular Component

Suppose you have a simple Angular component:

// app.component.ts
import { Component } from '@angular/core';

@Component({
  selector: 'app-root',
  template: `<h1>Hello {{ name }}!</h1>`
})
export class AppComponent {
  name = 'World';
}

To test this component:

  1. Import the Necessary Modules:
// app.component.spec.ts
import { TestBed } from '@angular/core/testing';
import { AppComponent } from './app.component';
  1. Configure the Testing Module:
describe('AppComponent', () => {
  beforeEach(async () => {
    await TestBed.configureTestingModule({
      declarations: [AppComponent]
    }).compileComponents();
  });

  it('should create the app', () => {
    const fixture = TestBed.createComponent(AppComponent);
    const app = fixture.componentInstance;
    expect(app).toBeTruthy();
  });
});
  1. Write Test Cases:
it(`should have as title 'World'`, () => {
  const fixture = TestBed.createComponent(AppComponent);
  const app = fixture.componentInstance;
  expect(app.name).toEqual('World');
});

it('should render title in a h1 tag', () => {
  const fixture = TestBed.createComponent(AppComponent);
  fixture.detectChanges();
  const compiled = fixture.nativeElement;
  expect(compiled.querySelector('h1').textContent).toContain('Hello World!');
});

5. Testing Angular Services:

Angular services can be tested without the need for a browser environment. Here’s an example:

import { TestBed } from '@angular/core/testing';
import { DataService } from './data.service';

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

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

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

  it('should return expected items (HttpClient called once)', (done: DoneFn) => {
    service.getItems().subscribe(items => {
      expect(items).toEqual(['first', 'second', 'third']);
      done();
    });
  });
});

6. Mocking Dependencies:

Angular provides the MockBackend service that allows you to mock HTTP requests and responses during testing. This is particularly useful for isolating components and services that depend on external services.

import { TestBed } from '@angular/core/testing';
import { HttpClientTestingModule, HttpTestingController } from '@angular/common/http/testing';
import { DataService } from './data.service';

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

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

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

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

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

  it('should return expected result (multiple calls)', () => {
    const expectedResult = [{ id: 1, name: 'First' }, { id: 2, name: 'Second' }];

    service.getItems().subscribe(result => {
      expect(result.length).toBe(2);
      expect(result).toEqual(expectedResult);
    });

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

7. Running Tests:

You can run Angular unit tests from the command line using the ng test command. This command will start Karma and run all the tests located in your project.

8. Code Coverage:

Karma can generate a code coverage report, which shows the percentage of your application's code that is covered by tests. This is useful for identifying untested parts of your application.

To generate a coverage report, use the --code-coverage option:

ng test --code-coverage

The coverage report will be generated in the coverage folder of your project.

Conclusion:

Angular’s built-in testing framework, combined with Jasmine and Karma, provides a powerful and flexible toolset for testing your Angular applications. By writing and maintaining thorough unit tests, you can ensure that your application is robust, reliable, and maintainable. Effective use of dependency injection and mocking can help isolate and test individual components and services in isolation, ensuring that they work as expected.




Angular Unit Testing with Jasmine and Karma: A Step-by-Step Guide for Beginners

Unit testing is a foundational practice in software development that ensures individual components or units of code work as expected. In the context of web applications, Angular provides a robust framework to build components, services, and other core constructs efficiently. Testing these units systematically is essential and can be achieved with Jasmine, a behavior-driven JavaScript testing framework, and Karma, a test runner that drives the tests.

This step-by-step guide will walk you through setting up unit tests in an Angular application using Jasmine and Karma, along with understanding the data flow in the process.

Step 1: Setting Up Your Angular Project

Before we dive into writing tests, let's ensure you have an Angular application ready. If you don’t already have one, you can quickly create a new Angular project using Angular CLI.

  1. Install Angular CLI:

    npm install -g @angular/cli

  2. Create a New Angular Project:

    ng new my-angular-app
cd my-angular-app

Step 2: Exploring Initial Test Setup

Angular CLI comes pre-configured with Jasmine and Karma. The necessary configurations are added to help you start testing immediately.

  • test.ts: This file is the entry point to your tests, importing libraries like Jasmine and Angular testing utilities.
  • karma.conf.js: This configuration file instructs Karma on which files to test, which browsers to use, and how to report the results.
  • angular.json: This file contains the scripts to run tests and specifies the root testing files.

Step 3: Writing Your First Unit Test

Let's create a simple service to demonstrate unit testing.

  1. Generate a Service:

    ng generate service example

  2. Implement a Method in the Service: Open src/app/example.service.ts and add a method.

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

@Injectable({
  providedIn: 'root'
})
export class ExampleService {

  constructor() { }

  addNumbers(a: number, b: number): number {
    return a + b;
  }
}

  3. Write a Test for the Service: Open src/app/example.service.spec.ts.

    import { TestBed } from '@angular/core/testing';
import { ExampleService } from './example.service';

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

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

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

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

Step 4: Running the Tests

To run the tests, use the following command:

ng test

This command will launch Karma, open a browser window, and execute the tests. You should see the test results in the console and in the browser window.

Step 5: Understanding the Data Flow

Here’s a brief overview of how the data flows through the testing process:

  1. Setup:

    • The beforeEach block in the test setup configures a testing module using TestBed.configureTestingModule({}).
    • It also instantiates the service with TestBed.inject(ExampleService);, providing a clean instance for every test.

  2. Testing:

    • The it block defines individual tests.
    • You can use expect statements to assert conditions or outcomes.

  3. Execution:

    • Karma runs the tests in a browser environment.
    • Jasmine framework orchestrates the tests and provides the assertion framework.

  4. Output:

    • The results are displayed in both the terminal and the browser.
    • For failed tests, Jasmine provides detailed error messages.

Step 6: Integrating Tests into Your Workflow

  • Continuous Integration (CI): Integrate your tests into a CI pipeline to ensure that tests are run with every commit.
  • Code Coverage: Configure Karma to report code coverage to ensure that you are testing all parts of your application.

Conclusion

Unit testing with Jasmine and Karma in Angular is a powerful way to ensure the reliability and correctness of your application. By following these steps, you can begin to write and run unit tests, understand the underlying data flow, and integrate tests into your development workflow. As you become more familiar, you'll find that testing becomes an integral part of writing robust and maintainable code.




Top 10 Questions and Answers on Angular Unit Testing with Jasmine and Karma

1. What is Unit Testing in Angular Applications? Unit testing in Angular applications involves testing the smallest units of source code to verify their correctness. In Angular, these units are typically individual components, services, pipes, and directives. Unit tests ensure that each unit performs as expected, helping to catch issues early in the development process.

**2. What are Jasmine and Karma? Jasmine is a powerful behavior-driven JavaScript testing framework that is commonly used for unit testing Angular applications. It provides a rich, human-readable syntax to define test cases. Karma, on the other hand, is a test runner that handles the execution of Jasmine tests across different browsers. It compiles the Angular code, runs the tests, and reports the results.

3. How do you set up Jasmine and Karma in an Angular project? Angular CLI comes with Jasmine and Karma configured by default when you create a new project. To install them manually in an existing project, you would:

  • Install Jasmine: npm install jasmine --save-dev
  • Install Karma: npm install karma karma-chrome-launcher karma-jasmine karma-jasmine-html-reporter --save-dev
  • Generate a Karma configuration file: npx karma init karma.conf.js
  • Integrate Jasmine and Karma by configuring the karma.conf.js file to point to your tests.

4. What are some of the key features and benefits of using Jasmine for unit testing in Angular? Jasmine offers several key features that make it ideal for unit testing in Angular:

  • Synchronous and Asynchronous Execution: Jasmine supports asynchronous testing, which is crucial for testing asynchronous operations like HTTP requests.
  • Readable Syntax: Its syntax is clear and easy to understand, making it accessible for developers.
  • Mocking: Jasmine provides built-in functions like spyOn() for creating and tracking mocks, which are essential for isolating dependencies.
  • 豐富 Matchergs: A comprehensive set of matchers allows you to write effective and expressive tests.

5. Can you explain how to create a simple test for a component in Angular using Jasmine and Karma? Sure, here’s an example of a simple test for an Angular component:

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

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

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

  beforeEach(() => {
    fixture = TestBed.createComponent(AppComponent);
    component = fixture.componentInstance;
    fixture.detectChanges();
  });

  it('should create app component', () => {
    expect(component).toBeTruthy();
  });

  it('should have as title "AngularUnitTest"', () => {
    expect(component.title).toEqual('AngularUnitTest');
  });

  it('should render title in a h1 tag', () => {
    const compiled = fixture.nativeElement;
    expect(compiled.querySelector('h1').textContent)
      .toContain('Welcome to AngularUnitTest!');
  });
});

6. How can you stub or mock services in Angular unit tests? Mocking services in unit tests is critical for isolating components and ensuring that tests are not affected by external dependencies. Here’s how to create and use mocks:

import { TestBed } from '@angular/core/testing';
import { HttpClientTestingModule } from '@angular/common/http/testing';
import { MyComponent } from './my.component';
import { MyService } from './my.service';

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

  beforeEach(() => {
    const mockMyService = {
      myMethod: jasmine.createSpy('myMethod').and.returnValue(Promise.resolve(true))
    };

    TestBed.configureTestingModule({
      imports: [HttpClientTestingModule],
      declarations: [MyComponent],
      providers: [{
        provide: MyService, useValue: mockMyService
      }]
    });

    service = TestBed.inject(MyService);
  });

  it('should call myMethod', () => {
    const fixture = TestBed.createComponent(MyComponent);
    const component = fixture.componentInstance;

    component.someMethod();
    expect(service.myMethod).toHaveBeenCalled();
  });
});

7. What are test spies and how are they used in Jasmine? Test spies are objects that keep track of the methods used in tests, including arguments passed and return values. They help verify that specific methods are called with the correct parameters and help in mocking functions.

Here’s an example:

it('should test method with parameters', () => {
  const myObj = {
    myMethod: function(param) {
      console.log('Provided param:', param);
    }
  };

  spyOn(myObj, 'myMethod');

  myObj.myMethod('test');

  expect(myObj.myMethod).toHaveBeenCalledWith('test');
});

8. How do you test Angular services that make HTTP requests using Jasmine and Karma? When testing Angular services that make HTTP requests, you can use HttpClientTestingModule to mock HTTP requests.

import { TestBed, waitForAsync } from '@angular/core/testing';
import { HttpClientTestingModule, HttpTestingController } from '@angular/common/http/testing';
import { MyService } from './my.service';

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

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

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

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

  it('should retrieve data via GET', waitForAsync(() => {
    const testData = { id: 1, name: 'Test Data' };

    service.getData(1).subscribe(data => {
      expect(data).toEqual(testData);
    });

    const req = httpMock.expectOne(`https://api.example.com/data/1`);
    expect(req.request.method).toBe('GET');
    req.flush(testData);
  }));
});

9. How do you handle asynchronous code in Jasmine tests? Asynchronous operations like HTTP requests, timers, and promises need proper handling in tests. Jasmine provides several methods for this:

it('it should handle promise', async () => {
  const value = await service.asyncMethod();
  expect(value).toBe('expectedValue');
});

it('it should handle callback with done()', (done) => {
  service.getMethodWithCallback(() => {
    expect(true).toBe(true);
    done();
  });
});

it('it should timeout', () => {
  setTimeout(() => {
    expect(true).toBe(true);
  }, 100);
  jasmine.clock().install();
  jasmine.clock().tick(101); // Fast-forward time to 101ms
  jasmine.clock().uninstall();
});

10. How do you run your tests with Karma? To run your tests with Karma, you can execute the following command in your terminal:

  • npm run test or ng test

This command compiles the application and runs the tests configured in karma.conf.js. Karma will open a browser window and execute the Jasmine tests, displaying the results directly in the browser.

By leveraging these top 10 questions and answers, developers can effectively set up, run, and manage unit tests in Angular applications using Jasmine and Karma, ensuring that their Angular projects are well-tested and maintainable.