not really sure about this, as I have to rely on a build. I think it would be better to let users do options.dispatcherFactory(...) as OpenTelemetryDispatcherFactory is now exposed

one way we use for cleanup is

deferCleanup requires AutoCloseable which is not the case for Dispatcher or Subscription.

Also this is to test properly this proxy

  // public void closeDispatcher(Dispatcher dispatcher)
  private Object closeDispatcher(Method method, Object[] args) throws Throwable {
    if (method.getParameterCount() == 1
        && args[0] instanceof Proxy
        && Proxy.getInvocationHandler(args[0]) instanceof OpenTelemetryDispatcher) {
      args[0] = ((OpenTelemetryDispatcher) Proxy.getInvocationHandler(args[0])).getDelegate();
    }

    return invokeMethod(method, delegate, args);
  }

Will the cleanup propagate the error to the test in case this is failing? Because this means that we didn't "unwrap" the otel wrapper, which would fail at runtime

as per the intended cleanup, it's declared in the abstract parent class

  @AfterAll
  static void afterAll() throws InterruptedException, TimeoutException {
    connection.drain(Duration.ZERO);
    natsContainer.close();
  }

You should assign message to the message return value otherwise this method will end up returning null which is not what it should be doing. You can verify this by modifying your test to assert on the return value of this method.

totally forgot to test the return type of the Request methods. Thanks for the reminder!