我正在尋找使用HttpTestingController來測試我的服務通過HttpClient發送的POST請求中是否包含正確的字段集。網絡表格export class WebFormService {constructor(private httpClient: HttpClient) { }public submitForm(fields): Observable<any> {  const headers = new HttpHeaders()      .set('Content-Type', 'application/x-www-form-urlencoded');  const body = new HttpParams()    .set('_to',  environment.FORM_RECIPIENT)    .set('source', 'mysite');  for (let key of fields) {      body.set(key, fields[key]);  }  return this.httpClient.post(    environment.FORM_URL,    body,    {headers}  );}web-form.spec.tsit('sends a POST request via the HttpClient service', () => {    const testFields = {      name: 'test contributor',      message: 'my message',      email: '[email protected]'    };    webFormService.submitForm(testFields).subscribe();    const req = httpTestingController.expectOne(environment.FORM_URL);    expect(req.request.method).toEqual('POST');    expect(req.request.headers.get('Content-Type')).toEqual('application/x-www-form-urlencoded');    // Here I'd like to make assertions about the fields that data being posted.    req.flush('');});HttpRequest是url編碼的body，所以req.request.body是正確的url編碼的字符串。有什么好的選擇可以進行測試而無需對請求主體進行解碼和比較對象？