Why do we test HTTP requests with HTTPClientTestingModule if it doesn't make a real API request or increase code coverage?

There is a section on the Angular documentation which explains how to test HTTP requests; using the HttpClientTestingModule and HttpTestingController: https://angular.io/guide/http#testing-http-requests

On that section, they show you how to write a test which makes a HTTP request to a 'mock backend' here: https://angular.io/guide/http#expecting-and-answering-requests

Here is the code used from their example:

it('can test HttpClient.get', () => {
  const testData: Data = {name: 'Test Data'};

  // Make an HTTP GET request
  httpClient.get<Data>(testUrl)
    .subscribe(data =>
      // When observable resolves, result should match test data
      expect(data).toEqual(testData)
    );

  // The following `expectOne()` will match the request's URL.
  // If no requests or multiple requests matched that URL
  // `expectOne()` would throw.
  const req = httpTestingController.expectOne('/data');

  // Assert that the request is a GET.
  expect(req.request.method).toEqual('GET');

  // Respond with mock data, causing Observable to resolve.
  // Subscribe callback asserts that correct data was returned.
  req.flush(testData);

  // Finally, assert that there are no outstanding requests.
  httpTestingController.verify();
});

So my question is, what is the point of this kind of testing? AFAIK, it doesn't increase code coverage as it's not ran against a service and it doesn't call a real backend.