JavaScript 模拟函数在测试中返回未定义

Question

我正在尝试测试一些属于较大 React 应用程序一部分的 JavaScript 函数。他们大量使用模块模式，我怀疑这可能是我没有正确理解的。以下是我正在测试的脚本(与真实应用中实际使用的脚本几乎相同，只是真实应用中的 GetFeedData.getFeedData 调用了外部 API):

const GetFeedData = (function () {
let feed, feedId;
return {
    getFeedId: function (sub) {
        switch (sub) {
            case '1': case '2': case '3': case '4': case '5': case '6': case 'S':
                feedId = 1;
                break;
            case 'A': case 'C': case 'E':
                feedId = 26;
                break;
            case 'N': case 'Q': case 'R': case 'W':
                feedId = 16;
                break;
            case 'B': case 'D': case 'F': case 'M':
                feedId = 21;
                break;
            case 'L':
                feedId = 2;
                break;
            case 'G':
                feedId = 31;
                break;
            }
        },
        getFeedData: function () {
            if (feedId === 2) {
                feed = require('./MockData');
            }
        },
        feed: feed
    };
})();

const ReverseStop = (function () {
    let stopIdN, stopIdS;
    const stopData = require('../utils/stops');
    return {
        reverseStop: function (sub, stop) {
            var invalidEntries = 0;
            function filterByName (item) {
                if (item.stop_name == stop && typeof item.stop_id === 'string' && item.stop_id.charAt(0) == sub) {
                    return true;
                }
                invalidEntries ++;
                return false;
            }
            var stopObjs = stopData.filter(filterByName);
            for (var i = 0; i < stopObjs.length; i++) {
                if (stopObjs[i].stop_id.charAt(stopObjs[i].stop_id.length - 1) == 'N') {
                    stopIdN = stopObjs[i].stop_id;
                } else if (stopObjs[i].stop_id.charAt(stopObjs[i].stop_id.length - 1) == 'S') {
                    stopIdS = stopObjs[i].stop_id;
                }
            }
        },
        stopIdN: stopIdN,
        stopIdS: stopIdS
    };
})();

export const IsDelayN = (function () {
    let noDelay, yesDelay, nextArrival, delay;
    return {
        isDelay: function (sub, stop) {
            GetFeedData.getFeedId(sub);
            GetFeedData.getFeedData();
            ReverseStop.reverseStop(sub, stop);
            var arrivals = [];
            var delays = [];
            function dataFilter () {
                var invalidEntries = 0;
                var feedObjs = GetFeedData.feed.filter(function (feedObj) {
                    if (feedObj.entity.trip_update.stop_time_update.stop_id == ReverseStop.stopIdN) {
                        return feedObj.entity.trip_update.stop_time_update;
                    }
                });
                for (var i = 0; i < feedObjs.length; i++) {
                    arrivals.push(feedObjs.arrival.time.low);
                    delays.push(feedObjs.arrival.delay);
                }
            }
            nextArrival = Math.min(...arrivals);
            var delayIndex = arrivals.indexOf(nextArrival);
            delay = delays.delayIndex;
            if (delay === null || Math.ceil(delay / 60) <= 5) {
                noDelay = Math.ceil((nextArrival - GetFeedData.feed.header.timestamp.low) / 60);
            } else {
                yesDelay = Math.ceil(delay / 60);
            }
        },
        noDelay: noDelay,
        yesDelay: yesDelay,
        nextArrival: nextArrival 
    };
})();

export const IsDelayS = (function () {
    let noDelay, yesDelay, nextArrival, delay;
    return {
        isDelay: function (sub, stop) {
            GetFeedData.getFeedId(sub);
            GetFeedData.getFeedData();
            ReverseStop.reverseStop(sub, stop);
            var arrivals = [];
            var delays = [];
            function dataFilter () {
                var invalidEntries = 0;
                var feedObjs = GetFeedData.feed.filter(function (feedObj) {
                    if (feedObj.entity.trip_update.stop_time_update.stop_id == ReverseStop.stopIdS) {
                        return feedObj.entity.trip_update.stop_time_update;
                    }
                });
                for (var i = 0; i < feedObjs; i++) {
                    arrivals.push(feedObjs.arrival.time.low);
                    delays.push(feedObjs.arrival.delay);
                }
            }
            nextArrival = Math.min(...arrivals);
            var delayIndex = arrivals.indexOf(nextArrival);
            delay = delays.delayIndex;
            if (delay === null || Math.ceil(delay / 60) <= 5) {
                noDelay = Math.ceil((nextArrival - GetFeedData.feed.header.timestamp.low) / 60);
            } else {
                yesDelay = Math.ceil(delay / 60);
            }
        },
        noDelay: noDelay,
        yesDelay: yesDelay,
        nextArrival: nextArrival
    };
})();

我试图做的是分离出我的函数，这样我就可以在导出的函数中调用几个较短的函数，而不是一两个极长的函数。因为我需要在导出函数中调用几个变量 - GetFeedData.feed、ReverseStop.stopIdN 和 ReverseStop.stopIdS，所以我假设模块模式是比使用回调更好的方法。我可能完全错了。

在我的测试中，我尝试将 noDelay、nextArrival 和 delay 记录到控制台以查看它们是否已定义。我正在使用 Jest，如果该信息有帮助的话。我现在将省略测试的其他部分，因为它们似乎不相关(如果错误，请纠正我)，但这是该部分:

it('correctly takes input at beginning of api logic and outputs expected values at end', () => {
    IsDelayN.isDelay('L', 'Lorimer St');
    IsDelayS.isDelay('L', 'Lorimer St');

    expect(IsDelayN.noDelay).toBeTruthy();
    expect(IsDelayN.yesDelay).toBeFalsy();
    expect(IsDelayS.noDelay).toBeTruthy();
    expect(IsDelayS.yesDelay).toBeFalsy();
    console.log('IsDelayN noDelay: ' + IsDelayN.noDelay);
    console.log('IsDelayN nextArrival: ' + IsDelayN.nextArrival);
    console.log('IsDelayN delay: ' + IsDelayN.delay);
    console.log('IsDelayS noDelay: ' + IsDelayS.noDelay);
    console.log('IsDelayS nextArrival: ' + IsDelayS.nextArrival);
    console.log('IsDelayS delay: ' + IsDelayS.delay);
});

我的 console.log() 之前的测试都通过了，但每个 console.log() 都显示 undefined 。此外，我的 React 组件实际调用的脚本也得到了相同的结果。如果未定义这些变量，我将组件设置为呈现 null，而这正是发生的情况。

非常感谢任何有助于理解这一点的帮助。

Answer 1

您没有正确设置模块，当设置成员值时您应该改变对象，现在您只需设置一个变量值。

以下内容应该适合您:

    var module = (function(){
      const ret = {
        mutateSomething:function(value){
          //set otherValue on the object returned (mutate ret)
          ret.otherValue = value;
        }
        ,otherValue:undefined
      };//create the object first
      return ret;//then return the object
    }())//IIFE

    console.log("before mutate:",module.otherValue);
    module.mutateSomething("Hello World");
    console.log("after mutate:",module.otherValue);