medium-in-memory-mongodb-node_jest.setup.ts

// jest.setup.ts
import {MongoMemoryServer} from 'mongodb-memory-server';
import {Collection, Db, MongoClient} from 'mongodb';
import {PERSON_COLLECTION} from './src/constants';

let mongo: MongoMemoryServer;
let mongoClient: MongoClient;
let db: Db;


/**
 * 1.
 * Initial setup step to be run ONCE BEFORE ALL test cases
 */
beforeAll(async () => {
    /**
     * 1.1
     * Start in-memory MongoDB
     */
    mongo = new MongoMemoryServer({});

    /**
     * 1.2
     * Set the MongoDB host and DB name as environment variables,
     * because the application expect it as ENV vars.
     * The values are being created by the in-memory MongoDB
     */
    process.env.MONGO_HOST = await mongo.getUri();
    process.env.MONGO_DB = await mongo.getDbName();

    /**
     * 1.3
     * Connect to our in-memory MongoDB, so we can do some initial setup/cleaning
     */
    mongoClient = await MongoClient.connect(process.env.MONGO_HOST);
    db = mongoClient.db(process.env.MONGO_DB);

    /**
     * 1.4
     * Create our 'persons' collection on the newly created MongoDB
     */
    await db.createCollection(PERSON_COLLECTION);
});

/**
 * 2.
 * Step to be run before each test case
 */
beforeEach(async () => {
    /**
     * 2.1
     * Get all collection in the MongoDB and remove all elements from them.
     * We do this to have a clean state between each test case so we don't introduce
     * side effects inside the test cases, affecting other test cases
     */
    const collections: Array<Collection> = await db.collections();
    await Promise.all(
        collections.map(
            (collection: Collection) => collection.deleteMany({}),
        ),
    );
});

/**
 * 3.
 * Final "cleanup" step to be run after all the test cases finished
 */
afterAll(async () => {
    /**
     * 3.1
     * Close connection to our MongoDB
     * Stop our in-memory MongoDB
     */
    await mongoClient.close();
    await mongo.stop();
});