Test own Mutiny operator

Question

I am new to reactive Programming and created my first own Mutiny operator like described in https://smallrye.io/smallrye-mutiny/guides/plug.

My operator is a collector, which collect x items in list and send the items if x is reached or when the stream is completed.

public class ListCollectorUntil<T> extends AbstractMultiOperator<T, List<T>> {

ListCollectorUntil(Multi<? extends T> upstream) {
    super(upstream);
}

public ListCollectorUntil(Multi<? extends T> upstream, int count) {
    this(upstream);
    this.count = count;
}

private int count;
private final List<T> bufferList = new ArrayList<>();
private final List<T> tempBufferList = new ArrayList<>();

@Override
public void subscribe(MultiSubscriber<? super List<T>> downstream) {
    upstream.subscribe().withSubscriber(new ListCollectorProcessor(downstream));
}

private class ListCollectorProcessor extends MultiOperatorProcessor<T, List<T>> {

    public ListCollectorProcessor(MultiSubscriber<? super List<T>> downstream) {
        super(downstream);
    }

    @Override
    public void onItem(T item) {
        bufferList.add(item);
        if (bufferList.size() >= count) {
            this.downstream.onItem(getUni());
        }
    }

    @Override
    public void onCompletion() {
        Subscription subscription = this.upstream.getAndSet(Subscriptions.CANCELLED);
        if (subscription != Subscriptions.CANCELLED) {
            this.downstream.onItem(getUni());
            this.downstream.onCompletion();
        }
    }

    private List<T> getUni() {
        tempBufferList.clear();
        tempBufferList.addAll(bufferList);
        bufferList.clear();
        return tempBufferList;
    }
}

When I started testing it with the following code:

void buffer_after5Inputs_uniShouldBeReturned() {
    Multi<List<Integer>> multi = Multi.createFrom().items(1, 2, 3, 4, 5, 6)
            .plug( integerMulti -> new Buffer<>(integerMulti, 4));
    multi.subscribe().with(
            integerList -> System.out.println(integerList),
            failur -> System.out.println(failur),
            () -> System.out.println("completed")
    );
    AssertSubscriber<List<Integer>> assertSubscriber =
            multi.subscribe().withSubscriber(AssertSubscriber.create(2))
                    .assertCompleted()
            .assertItems(Arrays.asList(1, 2, 3, 4), Arrays.asList(5, 6));
}

FROM my first subscriber I get: [1, 2, 3, 4] [5, 6] completed But the Assertsubscriber seams to get no events, neither onItem nor onCompleted Did I make a mistake somewhere?

score 1 · Answer 1 · answered Mar 13 '21 at 10:09

After a while I figured out which mistake I made:

I didn't use the AssertSubscriber correctly: The create(int) describes how many events get requested from the emitter. In my case I need 6 Events

I didn't make a deep copy of my list, rather changed to previous List with my new Values. This seams like, that the event is not correctly recorded, but the values of the list, which the event is pointing to, is changed. Therefore, the correct values are shown. I changed my code from:

 private List<T> getUni() {
    tempBufferList.clear();
    tempBufferList.addAll(bufferList);
    bufferList.clear();
    return tempBufferList;

to

private List<T> getUni() {
        List<T> tempBufferList = new ArrayList<>(bufferList);
        bufferList = new ArrayList<>();
        return tempBufferList;
    }

And my List buffer works fine and the test is correctly run.

Test own Mutiny operator

1 Answers1