TypeError：undefined不是构造函数（评估setVariable.forEach）

Question

我试图用javascript茉莉花为此功能编写一个茉莉花测试，然后遇到此错误。

    window.mainFun = function(){      
        doSomething();
    } 

    function doSomething(){
         var a=["aa","ac","aa","ab","aa","ad","aa"];
         var c={}; 
         var b = new Set(groupTokens);
         var i=0
         b.forEach(function (item) {
            c["a"+(i++)] = item;
         }
         return c;
    }

然后我收到此错误：TypeeError: undefined is not a constructor (evaluating setVariable.forEach)

我试图这样测试此代码：

    describe("test suite", function() {
       it("test spec", function() {
           window.mainFun();
           expect(window.doSomething()).toEqual("{aa,ab,ac,ad}");
        });
    });

但是我遇到了同样的错误。