在通过Mocha测试asc/await时正确使用done()的方法

问题描述

我正在使用mocha练习基本的单元测试用例，并对 HOW 和 When 有点困惑，以使用 done()处理程序.

I am practicing basic unit test cases with mocha and a bit confused HOW and WHEN to use done() handler.

1. 如何使用done()?

下面是我无法使用done的示例代码:

Below is my sample code where I am not able to use done:

it('Testing insertDocumentWithIndex', async (done) => {
  try{
    var data = await db.insertDocumentWithIndex('inspections', {
      "inspectorId" : 1,
      "curStatus" : 1,
      "lastUpdatedTS" : 1535222623216,
      "entryTS" : 1535222623216,
      "venueTypeId" : 1,
      "location" : [
        45.5891279,
        -45.0446183
      ]
    })
    expect(data.result.n).to.equal(1);
    expect(data.result.ok).to.equal(1);
  }
  catch(e){
    logger.error(e);
    done(e);
  }
})

我跑步时失败，并引发错误-

When I run, it fails and throws an error-

但是，只有在失败的情况下才应调用done(原谅我，如果我说的是错误的话，我是初学者)，这是我在catch块中所做的，并返回到第二个返回Promise的地方，效果很好.参见下面的代码

But done should be called in case of failure only(forgive me if I am saying something incorrect, I am a beginner), which I have done in catch block and coming to the second point of returning a Promise, well that works fine. See below code

it('Testing insertDocumentWithIndex', async () => {
  return new Promise(async (resolve, reject) => {
    try{
      var data = await db.insertDocumentWithIndex('inspections', {
        "inspectorId" : 1,
        "curStatus" : 1,
        "lastUpdatedTS" : 1535222623216,
        "entryTS" : 1535222623216,
        "venueTypeId" : 1,
        "location" : [
          45.5891279,
          -45.0446183
        ]
      })
      expect(data.result.n).to.equal(1);
      expect(data.result.ok).to.equal(1);
      resolve()
    }
    catch(e){
      reject(e);
    }
  })
});

但这需要附加的Promise构造代码，但这不是问题.但这提出了另一个问题

But this requires an additional Promise construction code, not a problem though. But it raises another question

1. 何时应使用done?

对使用mocha编写测试用例的更好方法的任何帮助或建议都将有所帮助.

Any help or suggestion for a better approach for writing test cases with mocha will help.

推荐答案

正确的方法是不要将done与async..await一起使用. Mocha支持诺言，并且能够链接从it等函数返回的诺言. async函数是始终返回promise的函数的语法糖:

The correct way is to not use done with async..await. Mocha supports promises and is able to chain a promise that is returned from it, etc. functions. And async function is syntactic sugar for a function that always returns a promise:

it('Testing insertDocumentWithIndex', async () => {
    var data = await db.insertDocumentWithIndex('inspections', {
      "inspectorId" : 1,
      "curStatus" : 1,
      "lastUpdatedTS" : 1535222623216,
      "entryTS" : 1535222623216,
      "venueTypeId" : 1,
      "location" : [
        45.5891279,
        -45.0446183
      ]
    })
    expect(data.result.n).to.equal(1);
    expect(data.result.ok).to.equal(1);
})

仅在测试异步API时才需要

done，而不涉及承诺.即便如此，兑现承诺通常也会带来更清晰的控制流程.

done is needed only for testing asynchronous APIs than don't involve promises. Even then, converting to promises often results in cleaner control flow.

还有这个

it('Testing insertDocumentWithIndex', async () => {
  return new Promise(async (resolve, reject) => {
  ...

是promise构造反模式，由于async promise构造函数回调，这一点甚至更糟.

is promise construction antipattern, which is even worse because of async promise constructor callback.

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