How to restore mongo in chai mocha - node.js

Question

So I want to restore mongo database before tests begin.
I do this way:
const app = require("../app");
const chai = require("chai");
const mongoose = require("mongoose");
const User = require('../models/users');
const Region = require('../models/regions');
const testUsers = require('../testdata/users.json');
const testRegions = require('../testdata/regions.json');
describe('Restoring database', function () {
before(function(done) {
var promises = [
User.deleteMany().exec()
,Region.deleteMany().exec()
];
console.log('Cleaned database');
done();
});
before(function(done) {
testUsers.users.forEach(element => {
var ObjectId = mongoose.Types.ObjectId;
element._id = new ObjectId(element._id);
var newUser = new User(element);
newUser.save(function (err, result) {
if (err) {
console.log("err:",err);
}
});
});
console.log('Users added');
done();
});
before(function(done) {
testRegions.regions.forEach(element => {
var newRegion = new Region(element);
newRegion.save(function (err, result) {
if (err) {
console.log("err:",err);
}
});
});
console.log('Regions added');
done();
});
testdata/users.json and testdata/regions.json are simple json files including key/pair values.
Does this look good?
When I run
npm test
It does not give any error. And in the console I see this:
Restoring database
Cleaned database
Users added
Regions added
But when I look in database I get different results.
Sometimes everything looks good. All the rows are in the collections.
Sometimes a few rows are missing in one of the collections.
Sometimes one of the collections is empty.
This is a very strange behaviour.
I also tried to add in the variable "promises" each of the "newUser" and "newRegion" instead of executing them directly.
But I still get these strange results.
Whats the deal?

Answer 1

The issue is due to done() being called before the async statements/promises have completed.
Either use async/await or use Promises and only call done() when your async statements/promises have completed.
For example:
No done() call as we using await statements which will wait till each statement completes before continuing:
before(async function() {
let userResult = await User.deleteMany();
let regionResult = wait Region.deleteMany();
console.log('Cleaned database');
});
Or use done() with promises:
before(function(done) {
User.deleteMany()
.then(result => {
console.log('Cleaned database');
done();
});
});
The syntax in your before example is not adding Promises at all, it is simply adding those functions to an array:
var promises = [
User.deleteMany().exec()
,Region.deleteMany().exec()
];
Take a look at the following related answer to help.