### 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
new TestResponseHandler(i)
            );
        }
        logger.debug("waiting for response");
        fail.set(randomBoolean());
        boolean await = allRequestsDone.await(5, TimeUnit.SECONDS);
        if (await == false) {
            logger.debug("now failing forcefully");
            fail.set(true);
            assertTrue(allRequestsDone.await(5, TimeUnit.SECONDS));
        }
        logger.debug("DONE");
        serviceC.close();
        
        
        
        serviceB.disconnectFromNode(nodeC);
        serviceA.disconnectFromNode(nodeC);
    }
    public void testRegisterHandlerTwice() {
        serviceB.registerRequestHandler(
            "internal:action1",
            randomFrom(ThreadPool.Names.SAME, ThreadPool.Names.GENERIC),
            TestRequest::new,
            (request, message, task) -> { throw new AssertionError("boom"); }
        );
        expectThrows(
            IllegalArgumentException.class,
            () -> serviceB.registerRequestHandler(
                "internal:action1",