为什么这个Karma / Jasmine测试不会发现参考错误？

Question

我有以下代码按照标题对书籍进行排序：

function alphabetizeBookNodes(a, b) {
  if (typeof a.title !== "undefined") {
    var aTitle = _removeArticles(a.title.toLowerCase()),
        bTitle = _removeArticles(b.title.toLowerCase());
  } else {
    var aTitle = _removeArticles(a.book.title.toLowerCase()),
        bTitle = _removeArticles(b.book.title.toLowerCase());
  }

  if (aTitle > bTitle) return 1;
  if (aTitle < bTitle) return -1; 
  return 0;
}

function _removeArticles(str) {
  words = str.split(" ");
  if(words.length <= 1) return str;
  if( words[0] == 'a' || words[0] == 'the' || words[0] == 'an' ) { 
    return words.splice(1).join("");
  }
  return str;
}

module.exports = {alphabetizeBookNodes: alphabetizeBookNodes};

在浏览器中，行words = str.split(" ");会抛出Uncaught ReferenceError: words is not defined。它应该是let words = ...。

我试图使用Karma / Jasmine测试触发该错误，如下所示：

describe("Utils", function() { 
  it('compares books by removing articles from the title', function() { 
    let alphabetizeBookNodes = require('../utils').alphabetizeBookNodes;

    const bookA = {'title': 'The Grapes of Wrath'};
    const bookB = {'title': 'Huckleberry Finn'};

    let compare = function(a, b) { 
      return alphabetizeBookNodes(a, b);
    } 

    let books = [bookB, bookA];
    let sortedBooks = books.sort(compare);

    expect(sortedBooks.length).toEqual(2);
    expect(sortedBooks[0]).toEqual(bookA);
    expect(sortedBooks[1]).toEqual(bookB);
  });
});

为什么此测试不会触发ReferenceError？如何重写此测试以便它能够捕获用户在浏览器中遇到的此错误？