Javascript Mock external API with SinosJS not working

I was trying to mock an external API for my unit tests with the SinonJs framework. For mocking the API I use the fake saver from SinonJS (http://ift.tt/1RRkcyz) Unfortunately I was not able at the moment to send any request to my fake server... Does anybody know what I'm doing wrong in my test:

import expect from 'expect';
import { searchForProducts } from 'api/ProductAPI';
import emptyResults from 'api/ProductAPI_EmptyResult.json';

describe('ProductAPI', () => {
  let server;

  before(function () {
    server = sinon.fakeServer.create();
    server.respondWith(
      "GET",
      "http://ift.tt/1VY9vNP",
      [200, { "Content-Type": "application/json" }, JSON.stringify(emptyResults)]
    );
  });

  it('product search with working API ', () => {

    server.respond();

    searchForProducts('tv').then(
      (data) => {
          console.log('success');
      },
      (error) => {
        console.log('error');
      });

    //dummy expect
    expect(
      'test'
    ).toEqual('test');
  });
});

Some information for the code: the searchForProducts method is a function which makes a rest call with the help of a HTTP client called axios(http://ift.tt/X7rcPX)

Thank you for your help!

Greetz