@Override
                        public void onCancel() {
                            super.onCancel();
                            thatCounter.countDown();
                        }
A testing server interceptor, that allows awaiting the completion of the server call that is otherwise closed
asynchronously.

@return A testing server interceptor bean.
tests/src/test/java/net/devh/boot/grpc/test/config/AwaitableServerClientCallConfiguration.java