@Override
  public CompletionStage<BeamFnApi.InstructionResponse> handle(
      BeamFnApi.InstructionRequest request) {
    LOG.debug("Sending InstructionRequest {}", request);
    CompletableFuture<BeamFnApi.InstructionResponse> resultFuture = new CompletableFuture<>();
    outstandingRequests.put(request.getInstructionId(), resultFuture);
    requestReceiver.onNext(request);
    return resultFuture;
  }
@Test
  public void testRequestSent() {
    String id = "instructionId";
    client.handle(BeamFnApi.InstructionRequest.newBuilder().setInstructionId(id).build());

    verify(mockObserver).onNext(any(BeamFnApi.InstructionRequest.class));
  }