茉莉花未定义函数

我在终端Expected undefined to be greater than 18.中收到错误消息 我已经创建了一个函数，并且正在期望函数中调用该函数。我需要将函数作为变量传递吗？

describe("Age Test", function() {
    it("It calculates age and the return value must be greater than 18", 
    function(){
        /* Define */
        function ageCalculator(yDD,yMM,yYY) {
            // Current date
            var today = new Date();
            var cDD = today.getDate();
            var cMM = today.getMonth()+1; //January is 0!
            var cYY = today.getFullYear();
            // Difference in date
            var dDD = cDD - yDD;
            var dMM = cMM - yMM;
            var dYY = cYY - yYY;
            if (dMM < 0) {
                dYY = dYY - 1;
            }
            if (dDD < 0) {
                dMM = dMM - 1;
            }
            dDD = dDD - 1;
            dMM = 12 + dMM;
            dDD = 30 + dDD;
        }
        /* Run Mock */
        expect(ageCalculator(27,4,1991)).toBeGreaterThan(18);
    });
});