@Test
  public void routerExceptionPipelineTest() throws Exception {
    FrontendTestRouter testRouter = new FrontendTestRouter(idConverterFactory);
    String exceptionMsg = TestUtils.getRandomString(10);
    testRouter.exceptionToReturn = new RouterException(exceptionMsg, RouterErrorCode.UnexpectedInternalError);
    doRouterExceptionPipelineTest(testRouter, exceptionMsg + " Error: " + RouterErrorCode.UnexpectedInternalError);
  }
Tests for cases where the {@link Router} returns valid {@link RouterException}.
@throws InstantiationException
@throws JSONException
ambry-frontend/src/test/java/com/github/ambry/frontend/FrontendRestRequestServiceTest.java