"before all" hook randomly showing up in my tests - node.js

Question

I'm currently running a stack that consists of Express and MongoClient with Mocha and Chai for testing. I'm working on writing test cases for my endpoint and am getting a random error that pops up from time to time. Below is a snippet of one of the suits I'm writing:
describe('Recipes with populated database', () => {
before((done) => {
var recipe1 = {"search_name": "mikes_mac_and_cheese", "text_friendly_name": "Mikes Mac and Cheese","ingredients": [{"name": "elbow_noodles","text_friendly_name": "elbow noodles","quantity": 12,"measurement": "oz"},{"name": "cheddar_cheese","text_friendly_name": "cheddar cheese","quantity": 6,"measurement": "oz"},{"name": "gouda_cheese","text_friendly_name": "gouda cheese","quantity": 6,"measurement": "oz"},{"name": "milk","text_friendly_name": "milk","quantity": 2,"measurement": "oz"}],"steps": ["Bring water to a boil","Cook noodels until al dente.","Add the milk and cheeses and melt down.","Stir constantly to ensure even coating and serve."],"course": ["dinner","lunch","side"],"prep_time": {"minutes": 15,"hours": 0},"cook_time":{"minutes": 25,"hours": 1},"cuisine": "italian","submitted_by": "User1","searchable": true};
db.collectionExists('recipes').then((exists) => {
if (exists) {
db.getDb().dropCollection('recipes', (err, results) => {
if (err)
{
throw err;
}
});
}
db.getDb().createCollection('recipes', (err, results) => {
if (err)
{
throw err;
}
});
db.getDb().collection('recipes').insertOne(recipe1, (err, result) => {
done();
});
});
});
The collectionExists() method simply takes in a name and returns a promise that is resolved to a true/false value. I've already done some debugging and it is working just fine. Where I am getting a problem is when I hit the section of the code where I call createCollection. I get an error about how the collection already exists thus leading to my tests failing. This appears to be happening on every third time I'm running my tests as well.
The purpose of all this is to ensure that my database collection called recipes is completely empty before I start testing so I'm not stuck with old data or in an uncontrolled environment.

Answer 1

You have a race condition between .createCollection and .insertOne. In other words, they start at the same time and go in parallel. There is no way to tell which will be done first.
The way .insert works in MongoDB is that if the collection is missing and you try inserting - it's going to create a collection. So if .insertOne is executed first - the collection is created and that is why you're getting the already exists error in an attempt to createCollection.
Due to the async nature of DB calls you'd have to place the subsequent calls inside the callback of a prev. one. This way there will be no parallel execution:
before((done) => {
var recipe1 = {/**/};
db.collectionExists('recipes')
.then((exists) => {
if (exists) {
// Drop the collection if it exists.
db.getDb().dropCollection('recipes', (err) => {
if (err) {
// If there's an error we want to pass it up to before.
done(err);
return;
}
// Just insert a first document into a non-existent collection.
// It's going to be created.
// Notice the done callback.
db.getDb().collection('recipes').insertOne(recipe1, done);
});
}
// If there were no such collection - simply insert the first doc to create it.
// Note that I'm passing before's done callback inside.
db.getDb().collection('recipes').insertOne(recipe1, done);
})
// We don't want to lose the error from this promise always.
.catch(err => done(err));
});
But. Actually, there is no need to drop and re-create a collection each time you run the tests. You can simply .remove all the objects in the before block. So probably the right solution would be:
before((done) => {
var recipe1 = {/**/};
const recipes = db.getDb().collection('recipes');
// Simply wipe out the data
recipes.remove({}, err => {
if (err) {
done(err);
return;
}
recipes.insertOne(recipe1, done);
});
});