如何解决"ReferenceError:期望未定义"?错误信息? [英] How can I solve "ReferenceError: expect is not defined" error message?

问题描述

我正在尝试用Mocha测试Javascript.我有以下代码段:

I am trying to test Javascript with mocha. I've this snippet of code:

describe('Array', function() {
    describe('indexOf()', function() {
        it("dovrebbe tornare -1 quando l'elemento non è presente", function() {
            expect([1,2,3].indexOf(4)).to.equal(-1)
        })
    })
})

和test/array.js文件. Mocha已安装

and a test/array.js file. Mocha was installed with

$ npm install -g mocha

我跑步时

$ mocha

我收到此错误:

$ mocha
․ 

0 passing (5ms)
1 failing

1) Array indexOf() dovrebbe tornare -1 quando l'elemento non è presente:
 ReferenceError: expect is not defined
  at Context.<anonymous> (/Users/simonegentili/Desktop/Javascipt Best Practice/test/array.js:4:4)
  at Test.Runnable.run (/usr/local/lib/node_modules/mocha/lib/runnable.js:211:32)
  at Runner.runTest (/usr/local/lib/node_modules/mocha/lib/runner.js:358:10)
  at /usr/local/lib/node_modules/mocha/lib/runner.js:404:12
  at next (/usr/local/lib/node_modules/mocha/lib/runner.js:284:14)
  at /usr/local/lib/node_modules/mocha/lib/runner.js:293:7
  at next (/usr/local/lib/node_modules/mocha/lib/runner.js:237:23)
  at Object._onImmediate (/usr/local/lib/node_modules/mocha/lib/runner.js:261:5)
  at processImmediate [as _immediateCallback] (timers.js:317:15)

推荐答案

Mocha是一个测试框架；您需要按照 https://mochajs.org/#assertions 状态提供自己的断言库.因此，expect确实是未定义的，因为您从未定义它.

Mocha is a test framework; you need to provide your own assertion lib as https://mochajs.org/#assertions states. Thus, expect is indeed undefined because you never defined it.

(我建议柴)

npm install chai

然后

(请参阅Amit Choukroune的评论指出实际上需要柴)

(see Amit Choukroune's comment pointing out to actually require chai)

然后

var expect = chai.expect;

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