@Test
public void testOperationFail() {

  RuntimeException expectedError = new RuntimeException("expected error");
  tracedCallable.call("test", responseObserver, callContext);
  MockServerStreamingCall<String, String> innerCall = innerCallable.popLastCall();
  innerCall.getController().getObserver().onError(expectedError);
  assertThat(responseObserver.getFinalError()).isEqualTo(expectedError);
  verify(tracer, times(1)).operationFailed(expectedError);
}