对调用承诺返回函数的递归方法进行单元测试

Posted 2023-03-13

【中文标题】对调用承诺返回函数的递归方法进行单元测试

【英文标题】：Unit testing a recursive method that calls a promise-returning function

【发布时间】：2017-05-08 05:22:33

【问题描述】：

下面是我正在尝试测试的代码的简化版本：一个定期清空的简单队列。对于队列中的每个号码，都会进行 HTTP POST 以将其发送到（在本例中为虚构的）API 地址。如果 POST 成功，则将号码移出队列并考虑下一个号码。

class Queue 
    queue: Array<number>;
    processingQueue: boolean;

    constructor(public $http: angular.IHttpService) 
        this.queue = new Array<number>();
        this.processingQueue = false;
    

    startQueueProcessor() 
        this.processingQueue = false;

        setInterval(() => 
            if (!this.processingQueue)
                this.processQueue();
        , 1000);
    

    postNumber(number: number): angular.IHttpPromise<> 
        return this.$http.post('http://mydummyurl.com/givemeanumber', number);
    

    processQueue(): void 
        this.processingQueue = true; // we are currently processing a queue, so make sure setInterval does not trigger another processing run

        if (this.queue.length !== 0)  // are there any numbers to deal with?
            const item = this.queue[0]; // get the first number in the queue

            this.postNumber(item) // POST it (returns a promise)
                .then(
                () =>  // if successful...
                    this.queue.shift(); // we've dealt with this item, so remove it from the queue
                    this.processQueue(); // check the queue again (recurses until all items have been dealt with)
                ,
                () =>  // if unsuccessful...
                    this.processingQueue = false; // something went wrong, so stop
                
                );
         else 
            this.processingQueue = false; // queue is empty, stop processing
        
    

    enqueue(number: number): void  // add a number to the queue
        this.queue.push(number);
    

我希望创建的测试将检查，在将三个项目添加到队列后，对 processQueue() 的一次调用将清空它。

类似这样的东西（在 Jasmine 中模拟）：

describe('queueing', () => 
    var queueService;

    beforeEach(inject((_$httpBackend_, $injector) => 
        httpBackend = _$httpBackend_;
        httpBackend.whenPOST().respond(200);

        queueService = $injector.get('queue');
    ));

    it('should clear queue completely when processQueue() is called once', () => 

        queueService.enqueue(1);
        queueService.enqueue(2);
        queueService.enqueue(3);

        expect(queueService.queue.length).toBe(3);

        queueService.processQueue();

        // somehow wait for processQueue() to complete

        expect(queueService.queue.length).toBe(0);
    );
);

我的问题是第二个expect() 总是失败并显示消息Expected 3 to be 0。我认为这是由于没有等待 postNumber() 返回的承诺，因此在调用第二个 expect() 时队列不为空。

如何等待processQueue() 完成，然后再尝试断言队列已被清空？

【参考方案1】：

您应该修改 processQueue 以返回 Promise。最简单的方法是使用 async 关键字标记方法，然后使用 await：

async processQueue(): Promise<void> 

    this.processingQueue = true; // we are currently processing a queue, so make sure setInterval does not trigger another processing run

    if (this.queue.length !== 0) 
     // are there any numbers to deal with?
        const item = this.queue[0]; // get the first number in the queue

        try
        
            await this.postNumber(item); // POST it (returns a promise)
            // if successful...
            this.queue.shift(); // we've dealt with this item, so remove it from the queue
            this.processQueue(); // check the queue again (recurses until all items have been dealt with)
        
        catch
        
                this.processingQueue = false; // something went wrong, so stop
        
     
    else 
    
        this.processingQueue = false; // queue is empty, stop processing
    

然后在你的测试中：

it('should clear queue completely when processQueue() is called once', async (done) => 

    queueService.enqueue(1);
    queueService.enqueue(2);
    queueService.enqueue(3);

    expect(queueService.queue.length).toBe(3);

    await queueService.processQueue();

    // somehow wait for processQueue() to complete

    expect(queueService.queue.length).toBe(0);

    done();
);    

希望这会有所帮助。

【讨论】：

感谢@Amid 的建议。我已经尝试过了，但出现以下错误：Error: Timeout - Async callback was not invoked within timeout specified by jasmine.DEFAULT_TIMEOUT_INTERVAL. 第一个断言正确关闭，但随后await 部分似乎没有返回任何内容并且它超时。

我可以看到两个原因。 http.post 无法到达主机并且操作超时。或者（这更有可能）angular.IHttpPromise 与打字稿使用的通用 A+ 承诺不兼容。转换示例见以下两个链接：codeproject.com/articles/1019920/…和***.com/questions/24611078/…