用玩笑的计时器测试redux-saga防抖动

Question

我有一个传奇，侦听模型更新并触发保存到网络，并在1秒钟后反跳：

export default function* graphModelUpdate() {
    const modelChangeDebounceTime = 1000;
    let task;

    while (true) {
        const action = yield take(IllustrationsActions.GRAPH_MODEL_CHANGED);
        if (task) {
            yield cancel(task);
        }
        task = yield fork(function* (payload) {
            yield call(delay, modelChangeDebounceTime);
            yield put(IllustrationsActions.apiUpdateGraph(payload));
        }, action.payload);
    }
}

然后，我根据redux-saga docs和jest docs regarding timers编写了此测试，用于测试传奇的效果而不是其实现：

jest.useFakeTimers();

describe('graphModelUpdate saga', () => {
    let dispatched;
    let mockState;
    let subscribers = [];
    const emitAction = (action) => {
        subscribers.forEach(cb => cb(action));
    };
    const options = {
        subscribe: callback => {
            subscribers.push(callback);
            return () => subscribers = subscribers.filter(cb => cb !== callback);
        },
        dispatch: (action) => dispatched.push(action),
        getState: () => mockState
    };

    beforeEach(() => {
        dispatched = [];
        mockState = {};
    });

    it('should listen for IllustrationsActions.GRAPH_MODEL_CHANGED and dispatch IllustrationsActions.apiUpdateGraph, debounced by 1 second', () => {
        runSaga(options, graphModelUpdate);
        emitAction(IllustrationsActions.graphModelChanged('model one'));
        emitAction(IllustrationsActions.graphModelChanged('model two'));
        emitAction(IllustrationsActions.graphModelChanged('model three'));
        expect(dispatched).toEqual([]);
        jest.runTimersToTime(1500);
        expect(dispatched).toEqual([
            IllustrationsActions.apiUpdateGraph('model three')
        ]);
    });
});

问题是，由于传奇使用了异步运行的fork，所以无论经过了多少假时间（expect），最终的jest.runTimersToTime(1500)都会在分派去抖动作之前执行，总是失败。

如何处理这种情况？

Answer 1

伪造的计时器正确地提前了时间，但是仍然有必要释放事件循环，以便生成器恢复执行，并且只有在我们可以继续执行期望之后才可以执行

关于不使用setTimeout的方法的示例（因为它已经被玩笑所嘲笑）：

jest.runTimersToTime(1500);
await Promise.resolve(); // generator resumes execution
expect(dispatched).toEqual([
   IllustrationsActions.apiUpdateGraph('model three')
]);