@Test
public void testValidCompletion() {

    engine = new Engine();
    List<Stage> stages = new ArrayList<>();
    stages.add((Stage.PublisherStage) Flowable::empty);
    stages.add((Stage.Map) () -> i -> (int) i + 1);
    stages.add(new Stage.FindFirst() {
    });
    Graph graph = () -> stages;
    assertThat(engine.buildCompletion(graph)).isNotNull();
}