Correct way to use done() while testing asyc/await with mocha

问题

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

How to use done() ?

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);
  }
})

When I run, it fails and throws an error-

Error: Timeout of 2000ms exceeded. For async tests and hooks, ensure "done()" is called; if returning a Promise, ensure it resolves.

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);
    }
  })
});

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

WHEN done should be used ?

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

回答1:

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);
})

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

And this

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

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

来源：https://stackoverflow.com/questions/52449202/correct-way-to-use-done-while-testing-asyc-await-with-mocha

标签

node.js

async-await

mocha