@Nonnull @Override
    public ProgressState call() {
        progTracker.reset();
        stateMachineStep();
        return progTracker.toProgressState();
    }
@Test
    public void when_doneItemOnInput_then_eventuallyDone() {
        // When
        init(singletonList(DONE_ITEM));

        // Then
        assertEquals(DONE, sst.call());
    }