then:
        1 * cancellationHandler.isCancellationRequested() >> false
        1 * workerLease.tryLock() >> true
        1 * workSource.executionState() >> WorkSource.State.MaybeWorkReadyToStart
        1 * workSource.selectNext() >> WorkSource.Selection.of(node)
        1 * worker.execute(node)
        1 * workSource.finishedExecuting(node, null)

        then:
        1 * cancellationHandler.isCancellationRequested() >> false

public interface WorkSource<T> {
    enum State {
        /**
         * There may be work ready to start. The worker thread should call {@link #selectNext()} to select the next item.
         * Note this does not mean that {@link #selectNext()} will necessarily return an item, only that it is likely to.
         * {@link #selectNext()} may not return an item, for example when some other worker thread takes the work.
         */
        MaybeWorkReadyToStart,