Unit Test with Express / Mocha / Mongodb Memory Server - node.js

Question

I would like to configure my project in order to run unit test for some API endpoints (that call the database). I'm using :
ExpressJS
MongoDB (no Mongoose)
Mocha / Chai
Mongodb Memory Server (to mock the DB)
// app.ts
export const app = express();
const port = process.env.PORT;
app.use("/my-route", myRoutes);
mongoConnect().then(() => {
app.listen(port, () => {
console.log(`Listening on port ${port}`);
});
});
// database.ts
export const mongoConnect = async () => {
try {
let MONGODB_URI = process.env.MONGODB_URI;
if (process.env.NODE_ENV === "test") {
const mongoServer = await MongoMemoryServer.create();
MONGODB_URI = mongoServer.getUri();
}
const client: MongoClient = await MongoClient.connect(MONGODB_URI);
_db = client.db("dbName");
_mongoClient = client;
if (process.env.NODE_ENV === "test") {
console.log("Connected to MongoDB Test");
} else {
console.log("Connected to MongoDB");
}
} catch (err) {
console.log("Error connecting to MongoDB:", err);
throw err;
}
};
export const getMongoClient = () => {
if (_mongoClient) {
return _mongoClient;
}
throw "Mongo client doesn't exist";
};
export const getDb = () => {
if (_db) {
return _db;
}
throw "No database found!";
};
// test.ts
let mongoClient: MongoClient;
let db: Db;
before(function (done) {
mongoConnect()
.then(() => {
db = getDb();
mongoClient = getMongoClient();
return db.createCollection("wordsCollection");
})
.then(() => {
db.collection("wordsCollection").insertMany(data);
})
.catch((err) => console.log(err))
.finally(() => done());
});
after(function (done) {
db.dropDatabase();
mongoClient.close().then(() => {
done();
});
});
it("test", async function () {
let res = await chai
.request(app)
.post("/my-route/hello")
.send({ excludeIds: [] });
expect(res.status).to.equal(200);
});
});
But it's not working...
If I call mongoConnect() in test.ts it console.log twice Connected to MongoDB Test. But if I don't call the function it throws me error because MongoClient is undefined.
I think await chai.request(app) already calls the database and server but I need to create Collection and Documents before. So I need to connect to the DB before the test.
Any help would be greatly appreciated.

Answer 1

I found a solution, I don't know if it's best practice but it works and is pretty easy, thanks to this post : https://stackoverflow.com/a/70285190/10547153.
I needed to add a condition in app.ts before making the connection to the database and the server in order to launch them only if it's called by Node itself.
if (require.main === module) {
mongoConnect().then(() => {
app.listen(port, () => {
console.log(`Listening on port ${port}`);
});
});
}
When a file is run directly from Node.js, require.main is set to its
module. That means that it is possible to determine whether a file has
been run directly by testing require.main === module.
Now I can connect to the mocked database from test.ts and only one connection will be triggered.