Mocha/Chai测试链接到函数返回断言错误

我正在尝试查找&更正challenge.js中的Javascript代码，使其通过Mocha&Chai按照spec.js中的规定进行测试……当我在终端中运行命令$ mocha spec.js时，我所做的任何尝试都无法使它通过测试。。。。为了提供更多信息，无论我对challenge.js做了什么更改，终端都会不断返回错误消息。

挑战.js

module.exports.linkTo = function(text, address) {   
  return "<a href='" + text + "'>" + address + "</a>"
};

Spec.js

var expect = require("chai").expect;
var challenge = require("./challenge.js");
describe("linkTo", function() {
  it("should be defined", function() {
    expect(challenge.linkTo).to.exist;
  });
  it("should return a valid link for Bloc", function() {
    expect(challenge.linkTo("Bloc", "http://www.bloc.io")).to.eql("<a       href='http://www.bloc.io'>Bloc</a>");
  });
});

终端返回的错误消息

linkTo
✓ should be defined 
1) should return a valid link for Bloc

  1 passing (11ms)
  1 failing
  1) linkTo should return a valid link for Bloc:
  AssertionError: expected '<a href=''Bloc''>http://www.bloc.io</a>' to deeply equal '<a href=''http://www.bloc.io''>Bloc</a>'
  + expected - actual
  +<a href='http://www.bloc.io'>Bloc</a>
  -<a href='Bloc'>http://www.bloc.io</a>
  at Context.<anonymous> (/home/vagrant/frontend-javascript-exercises/02-reading-mocha-tests/00-a-tested-function/spec.js:10:63)
  at callFn (/usr/local/lib/node_modules/mocha/lib/runnable.js:266:21)
  at Test.Runnable.run (/usr/local/lib/node_modules/mocha/lib/runnable.js:259:7)
  at Runner.runTest (/usr/local/lib/node_modules/mocha/lib/runner.js:387:10)
  at /usr/local/lib/node_modules/mocha/lib/runner.js:470:12
  at next (/usr/local/lib/node_modules/mocha/lib/runner.js:312:14)
  at /usr/local/lib/node_modules/mocha/lib/runner.js:322:7
  at next (/usr/local/lib/node_modules/mocha/lib/runner.js:257:23)
  at Object._onImmediate (/usr/local/lib/node_modules/mocha/lib/runner.js:289:5)
  at processImmediate [as _immediateCallback] (timers.js:336:15)

当我在终端中运行$ mocha spec.js时，有人能指出challenge.js中需要的更正吗？？？

提前感谢Lex