AssertionError: expected {} to be a function

Question

我第一次在 Chai 中使用 Mocha 时遇到了一个奇怪的错误。我以前用过的唯一框架是 Jasmine，如果它能帮助你找出我做错了什么的话。

我只是想确保我的构造函数不会引发错误。我已经能够将代码缩减为这个，但仍然出现错误：

class MyLib {
  constructor() {}
}

export default MyLib;

这是测试文件：

import chai from 'chai';
let { expect } = chai;

import MyLib from '../index';

describe('mylib-js', () => {
  describe('constructor', () => {
    it('should work', () => {
      expect(new MyLib()).to.not.throw();
    })
  });
});

这是摩卡的输出：

d:\path\to\mylib-js>mocha --require babel-core/register


  mylib-js
    constructor
      1) should work


  0 passing (23ms)
  1 failing

  1) mylib-js constructor should work:
     AssertionError: expected {} to be a function
      at Assertion.an (d:\path\to\mylib-js\node_modules\chai\lib\chai\core\assertions.js:169:10)

      at Assertion.assert (d:\path\to\mylib-js\node_modules\chai\lib\chai\utils\addChainableMethod.js:84:49)
      at Assertion.assertThrows (d:\path\to\mylib-js\node_modules\chai\lib\chai\core\assertions.js:1273:32)
      at Assertion.ctx.(anonymous function) [as throw] (d:\path\to\mylib-js\node_modules\chai\lib\chai\utils\addMethod.js:41:25)
      at Context.<anonymous> (test.js:10:4)
      at callFn (C:\Users\Myuser\AppData\Roaming\npm\node_modules\mocha\lib\runnable.js:315:21)
      at Test.Runnable.run (C:\Users\Myuser\AppData\Roaming\npm\node_modules\mocha\lib\runnable.js:308:7)
      at Runner.runTest (C:\Users\Myuser\AppData\Roaming\npm\node_modules\mocha\lib\runner.js:422:10)
      at C:\Users\Myuser\AppData\Roaming\npm\node_modules\mocha\lib\runner.js:533:12
      at next (C:\Users\Myuser\AppData\Roaming\npm\node_modules\mocha\lib\runner.js:342:14)
      at C:\Users\Myuser\AppData\Roaming\npm\node_modules\mocha\lib\runner.js:352:7
      at next (C:\Users\Myuser\AppData\Roaming\npm\node_modules\mocha\lib\runner.js:284:14)
      at Immediate._onImmediate (C:\Users\Myuser\AppData\Roaming\npm\node_modules\mocha\lib\runner.js:320:5)

我不知道错误输出中的 {} 从哪里来的。它想告诉我什么？

Answer 1

如异常消息所述，new MyLib 是对象而非函数。

它应该像这样才能很好地与 throw 断言一起工作。

expect( () => new MyLib).not.to.throw()

AssertionError: expected {} to be a function

AssertionError: expected {} to be a function

javascript

unit-testing

mocha.js

chai