mocha/sinon存根还原不工作

我的第一个节点测试脚本。我正在使用Mocha和Sinon测试最终发送到队列的函数。节点v8.1.3、Mocha 5.0.2、sinon 4.4.2。

var assert = require('assert');
var sinon = require('sinon');
var uut = require('../util');
var stub;

describe('processWantedItemToQueue', function() {
    beforeEach(function() {
      stub = sinon.stub(uut, 'processWantedItemToQueue').returns(true);
    });

    afterEach(function() {
      uut.processWantedItemToQueue.restore();
    });

    it('should not push the item to the queue', function() {
      assert.equal(uut.processWantedItemToValidQueue("a", "q1"), false);
    });

    it('should push the item to the queue', function() {
      assert.equal(uut.processWantedItemToValidQueue("a", "aws"), true);
    });
});

这是我的输出:

> mocha
  processWantedItemToQueue
ignoring queue q1
    ✓ should not push the item to the queue
    1) should push the item to the queue


  1 passing (34ms)
  1 failing

  1) processWantedItemToQueue
       should push the item to the queue:
     ReferenceError: processWantedItemToQueue is not defined
      at Object.processWantedItemToValidQueue (util.js:36:20)
      at Context.<anonymous> (test/test.js:20:24)

我对存根有些误解。为什么我的第二次测试没有找到存根?

我的util。js如下所示:

module.exports = {
  processWantedItem: function(item) {
  ...
  },
  processWantedItemToQueue: function(item, queue) {
  ...
  },
  processWantedItemToValidQueue: function(item, queue) {
  ...
  }
}