testSend_failToFetch() {
    const failedPromise = new Promise(() => {
      throw new Error('failed to fetch');
    });
    fetchMock(new Request('https://www.google.com', {
      headers: new Headers(),
      method: 'GET',
    })).$returns(failedPromise);

    mockControl.$replayAll();
    return new Promise((resolve) => {
      const xhr = factory.createInstance();
      xhr.open('GET', 'https://www.google.com', true /* opt_async */);
      xhr.onreadystatechange = () => {
        assertEquals(xhr.readyState, FetchXmlHttp.RequestState.DONE);
        assertEquals(0, xhr.status);
        assertEquals('', xhr.responseText);
        resolve();
      };
      xhr.send();
      assertEquals(xhr.readyState, FetchXmlHttp.RequestState.OPENED);

      mockControl.$verifyAll();
    });
  }
Verifies the send method in case of failure to fetch the url.
@return {!Promise<void>}