@Test
public void testOperationCancelled() {

  ApiStreamObserver<String> clientStream =
      tracedCallable.clientStreamingCall(outerResponseObsever, callContext);
  clientStream.onError(new CancellationException("explicitly cancelled"));
  innerCallable.responseObserver.onError(
      new CancelledException(
          "fake exception that would be generated by a client cancelling the rpc",
          null,
          FakeStatusCode.of(Code.CANCELLED),
          false));
  verify(tracer, times(1)).operationCancelled();
}