To mock HTTP requests in Angular unit tests, you can use the `HttpClientTestingModule` and `HttpTestingController` provided by Angular's testing utilities.

Here's an example to demonstrate how to mock an HTTP request in Angular:

Let's assume you have a service called `DataService` that makes HTTP requests using Angular's `HttpClient`: 

import { Injectable } from '@angular/core';
import { HttpClient } from '@angular/common/http';

@Injectable()
export class DataService {
  constructor(private http: HttpClient) {}

  fetchData(): Promise<string> {
    return this.http.get<string>('https://api.example.com/data').toPromise();
  }
}
Now, let's write a unit test for the `DataService` and mock the HTTP request: 

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 fetch data from the API', () => {
    const mockResponse = 'Mocked API response';

    service.fetchData().then((data) => {
      expect(data).toBe(mockResponse);
    });

    const req = httpMock.expectOne('https://api.example.com/data');
    expect(req.request.method).toBe('GET');
    req.flush(mockResponse);
  });
});
In the test above, we import `HttpClientTestingModule` and use it in the `TestBed.configureTestingModule()` to configure the testing module. We also inject the `HttpTestingController` to interact with the HTTP requests. Inside the test, we call the `fetchData` method of the `DataService` and assert on the response data. Then, we use `httpMock.expectOne()` to intercept the HTTP request and return a mock response using `req.flush()`. Finally, we use `httpMock.verify()` in the `afterEach` block to ensure that no unexpected requests were made. Conclusion : By using the `HttpClientTestingModule` and `HttpTestingController`, we can mock the HTTP requests and control their responses, allowing us to test the behavior of the service without making actual API calls. Note: Make sure to import the necessary testing utilities (`TestBed`, `HttpClientTestingModule`, `HttpTestingController`, etc.) from the appropriate packages (`@angular/core/testing`, `@angular/common/http/testing`, etc.) in your test files.