如何等待appendFile work Jest回调

Question

我有一个方法

private processWriteNextChunk(filePath: string): void {
    const nextChunk = this.data.get(filePath)?.shift();
    if (!nextChunk) return;
    appendFile(filePath, nextChunk.buffer, () => {
      nextChunk?.last ? this.data.delete(filePath) : this.emitWriteNextChunk(filePath);
    });
  }

我正在测试它，就像

  it('should call appendFile when chunk array is not empty and delete data pair if it was last chunk',() => {
let appendFileCallback;
const appendFileSpy = jest.spyOn(fs, 'appendFile').mockImplementation((path, data, callback) => {
  appendFileCallback = callback;
});
const data: IBufferChunk = { ...MOCK_DATA, last: true };
service.data.set(MOCK_PATH, [data]);
service.processWriteNextChunk(MOCK_PATH);

expect(appendFileSpy).toHaveBeenCalledWith(MOCK_PATH, data.buffer, appendFileCallback);
expect(service.data.size).toBe(0);


});

测试失败，错误为

​

​

这是因为this.data.delete(filePath)没有时间工作，我如何解决这个问题？

Answer 1

如果我理解正确的话，processWriteNextChunk代表一个异步操作。

因此，如果您将函数标记为async，并返回一个promise

 private async processWriteNextChunk(filePath: string): Promise<YOUR_TYPE> { 
    //...
    return appendFile(...)
 }

然后，您可以在jest it中使用await

it('should call appendFile when chunk array is not empty and call emitWriteNextChunk if it wasn\'t last chunk', async () => {
    //...
    await service.processWriteNextChunk(MOCK_PATH);
});

Answer 2

我的问题是mockImplementation函数改变了函数的工作方式，所以我的回调函数还没有被调用，所以我只是让它像这样

const appendFileSpy = jest
      .spyOn(fs, 'appendFile')
      .mockImplementation((path, data, callback) => {
        callback(null);
        appendFileCallback = callback;
      });

它工作得很好