@Override
  public UrlSigningService getUrlSigningService() {
    return new UrlSigningService() {
      @Override
      public String getSignedUrl(RestRequest restRequest) throws RestServiceException {
        if (getSignedUrlException != null) {
          throw getSignedUrlException;
        }
        return signedUrlToReturn;
      }

      @Override
      public boolean isRequestSigned(RestRequest restRequest) {
        return isRequestSigned;
      }

      @Override
      public void verifySignedRequest(RestRequest restRequest) throws RestServiceException {
        if (verifySignedRequestException != null) {
          throw verifySignedRequestException;
        }
      }
    };
  }
Implementation of {@link UrlSigningService} for tests in frontend.
ambry-frontend/src/test/java/com/github/ambry/frontend/FrontendRestRequestServiceTest.java