### Description

The `sendRequest` method is asynchronous and notifies a 
`TransportResponseHandler` when it completes the excecution
(successfully or unsuccessfully). 

When opening the connection we only catch `NodeNotConnectedException`
( https://github.com/elastic/elasticsearch/blob/main/server/src/main/java/org/elasticsearch/transport/TransportService.java#L719 ) which is currently fine as no implementations
throw other type of exception however, it'd be best to catch `Exception` here
so the `handler` gets notified of potential exceptions (as opposed to the caller
having to `try/catch` the call to `sendRequest`)
test/framework/src/main/java/org/elasticsearch/transport/AbstractSimpleTransportTestCase.java
responseReceived.incrementAndGet();
                }
            }
            @Override
            public void onRequestSent(
                DiscoveryNode node,
                long requestId,
                String action,
                TransportRequest request,
                TransportRequestOptions options
            ) {
                if (action.equals(ACTION)) {
                    requestsSent.incrementAndGet();
                }
            }
        }
        final CountingListener tracerA = new CountingListener();
        final CountingListener tracerB = new CountingListener();
        serviceA.addMessageListener(tracerA);
        serviceB.addMessageListener(tracerB);
        try {
            submitRequest(serviceA, nodeB, ACTION, TransportRequest.Empty.INSTANCE, EmptyTransportResponseHandler.INSTANCE_SAME).get();
        } catch (ExecutionException e) {
            assertThat(e.getCause(), instanceOf(ElasticsearchException.class));
            assertThat(ExceptionsHelper.unwrapCause(e.getCause()).getMessage(), equalTo("simulated"));
        }
        
        assertBusy(() -> {
            assertThat(tracerA.requestsReceived.get(), equalTo(0));
            assertThat(tracerA.requestsSent.get(), equalTo(1));