HttpTestingController finds two requests instead of one in Angular test with jest

Question

I am writing a unit test with jest for a service method that makes an http request to a local server that runs on json-server in localhost:3000

This is the service method:

fetchData() {
  return this.httpClient.get('http://localhost:3000/items');
}

And this is unit test for such method:

it('should retrieve an array of items', () => {
  service.fetchData().subscribe((response) => {
    expect(response).toEqual(mockItemList);
  });

  const request = httpController.expectOne({
    method: 'GET',
    url: 'http://localhost:3000/items'
  })

  request.flush(mockItemList);
});

Where:

• service is the service class
• mockItemList is a mocked array of items
• httpController is my instance of HttpTestingController.

When running the test, Jest returns the following error: Expected one matching request for criteria "Match method: GET, URL: http://localhost:3000/items", found 2 requests.

When I debug my application in Chrome, it correctly performs only 1 request, as seen in the Developer tools network tab and the service method is called only once.