### 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
String info;
        int resendCount;
        public TestRequest() {}
        public TestRequest(StreamInput in) throws IOException {
            super(in);
            info = in.readOptionalString();
            resendCount = in.readInt();
        }
        public TestRequest(String info) {
            this.info = info;
        }
        @Override
        public void writeTo(StreamOutput out) throws IOException {
            super.writeTo(out);
            out.writeOptionalString(info);
            out.writeInt(resendCount);
        }
        @Override
        public String toString() {
            return "TestRequest{" + "info='" + info + '\'' + '}';
        }
    }
    private static class TestResponse extends TransportResponse {