Tutorial

How To Test HttpClient Requests in Angular

Angular

Introduction

Angular’s HttpClient has a testing module, HttpClientTestingModule, that makes it possible for you to unit test HTTP requests.

Note: Since HttpClient is available only starting with Angular 4.3, the following applies to Angular 4.3+. Consult this introduction if you’re new to unit testing in Angular.

In this article, you will learn how to set up unit tests for an HTTP GET request using the HttpClientTestingModule. This will help demonstrate the capabilities of the testing module.

Prerequisites

To complete this tutorial, you will need:

This tutorial was verified with Node v16.2.0, npm v7.15.1, and @angular/core v12.0.4.

Step 1 — Setting Up the Project

For this post, we’ll be working with a service that gets data from an endpoint and a component that calls that service to populate a list of users in the component’s OnInit hook.

You can use @angular/cli to create a new project:

  • ng new angular-httpclienttest-example

Then, navigate to the newly created project directory:

  • cd angular-httpclienttest-example

Create a data.service.ts:

  • ng generate service data

And have it communicate with JSON Placeholder:

src/app/data.service.ts
import { Injectable } from '@angular/core';
import { HttpClient, HttpRequest } from '@angular/common/http';

@Injectable({ ... })
export class DataService {
  url = 'https://jsonplaceholder.typicode.com/users';

  constructor(private http: HttpClient) { }

  getData() {
    const req = new HttpRequest('GET', this.url, {
      reportProgress: true
    });

    return this.http.request(req);
  }
}

Then, modify the app.component.ts file:

src/app.component.ts
import { Component, OnInit } from '@angular/core';
import { HttpEvent, HttpEventType } from '@angular/common/http';

import { DataService } from './data.service';

@Component({ ... })
export class AppComponent implements OnInit {
  users: any;

  constructor(private dataService: DataService) {}

  ngOnInit() {
    this.populateUsers();
  }

  private populateUsers() {
    this.dataService.getData().subscribe((event: HttpEvent<any>) => {
      switch (event.type) {
        case HttpEventType.Sent:
          console.log('Request sent!');
          break;
        case HttpEventType.ResponseHeader:
          console.log('Response header received!');
          break;
        case HttpEventType.DownloadProgress:
          const kbLoaded = Math.round(event.loaded / 1024);
          console.log(`Download in progress! ${kbLoaded}Kb loaded`);
          break;
        case HttpEventType.Response:
          console.log('Done!', event.body);
          this.users = event.body;
      }
    });
  }
}

And add the HttpClientmodule to app.module.ts:

src/app.module.ts
import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { HttpClientModule } from '@angular/common/http';

import { AppComponent } from './app.component';

@NgModule({
  declarations: [
    AppComponent
  ],
  imports: [
    BrowserModule,
    HttpClientModule
  ],
  providers: [],
  bootstrap: [AppComponent]
})
export class AppModule { }

At this point, you will have an Angular project with a service and client.

Step 2 — Adding Tests

Now we’ll setup a spec file for our data service and include the necessary utilities to test out the HttpClient requests. On top of HttpClientTestingModule, we’ll also need HttpTestingController, which makes it easy to mock requests:

data.service.spec.ts
import { TestBed, inject } from '@angular/core/testing';
import { HttpEvent, HttpEventType } from '@angular/common/http';
import {
  HttpClientTestingModule,
  HttpTestingController
} from '@angular/common/http/testing';

import { DataService } from './data.service';

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

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

We use the inject utility to inject the needed services into our test.

With this in place, we can add our test logic:

data.service.spec.ts
import { TestBed, inject } from '@angular/core/testing';
import { HttpEvent, HttpEventType } from '@angular/common/http';
import {
  HttpClientTestingModule,
  HttpTestingController
} from '@angular/common/http/testing';

import { DataService } from './data.service';

describe('DataService', () => {
  beforeEach(() => {
    TestBed.configureTestingModule({
      imports: [HttpClientTestingModule],
      providers: [DataService]
    });
  });
  it(
    'should get users',
    inject(
      [HttpTestingController, DataService],
      (httpMock: HttpTestingController, dataService: DataService) => {
        const mockUsers = [
          { name: 'Alice', website: 'example.com' },
          { name: 'Bob', website: 'example.org' }
        ];

        dataService.getData().subscribe((event: HttpEvent<any>) => {
          switch (event.type) {
            case HttpEventType.Response:
              expect(event.body).toEqual(mockUsers);
          }
        });

        const mockReq = httpMock.expectOne(dataService.url);

        expect(mockReq.cancelled).toBeFalsy();
        expect(mockReq.request.responseType).toEqual('json');
        mockReq.flush(mockUsers);

        httpMock.verify();
      }
    )
  );
});

There’s quite a bit going on, so let’s break it down:

  • First we define a couple of mock users that we’ll test against.
  • We then call the getData method in the service that we’re testing and subscribe to returned observable.
  • If the HttpEventType is of type Response, we assert for the response event to have a body equal to our mock users.
  • We then make use of the HttpTestingController (injected in the test as httpMock) to assert that one request was made to the service’s url property. If no request is expected, the expectNone method can also be used.
  • We can now make any number of assertions on the mock request. Here we assert that the request hasn’t been canceled and the response is of type json. Additionally, we could assert the request’s method (GET, POST, …)
  • Next we call flush on the mock request and pass in our mock users. The flush method completes the request using the data passed to it.
  • Finally, we call the verify method on our HttpTestingController instance to ensure that there are no outstanding requests to be made.

For the purposes of this tutorial, you can comment out app.component.spec.ts.

See the result of your testing by running the following command:

  • ng test

Open the test results in the browser:

Output
1 spec, 0 failures, randomized with seed 26321 DataService should get users

It will display a successful test message.

Conclusion

In this article, you learned how to set up unit tests for an HTTP GET request using the HttpClientTestingModule.

If you’d like to learn more about Angular, check out our Angular topic page for exercises and programming projects.

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