void invokeOnSubscribe() {
            // Call the subscriber.onSubscriber() with the mock Subscription to emulate
            // that the delegate triggers onSubscribe().
            subscriberWrapper.onSubscribe(subscription);
        }
Tests if {@link PublisherBasedStreamMessage#abort()} prohibits further subscription.
core/src/test/java/com/linecorp/armeria/common/stream/PublisherBasedStreamMessageTest.java