Endpoint Testing Node Express API with MySql

I am working on an api using express which interfaces with a MySQL database to store user credentials.

I have an endpoint for registering users, and another for logging in. When I test these in Postman they work as expected.

I want to add unit tests to my API to test these endpoints which I can then integrate with a CI in the future.

I followed this guide to add endpoint testing using jest and supertest. This works somewhat but it is not an ideal solution. Ideally I want to use an in memory database instead of my actual SQL connection to test so that I can use a fresh database state for each test. I am struggling to find info online for how to achieve this in express.

Here is how I am currently querying my database to find a user by username.

const connection = require("./db.js");
User.getByUsername = (username, result) => {
  connection.query(
    `SELECT * FROM users WHERE username = "${username}"`,
    (err, res) => {
      if (err) {
        result(
          {
            status: 500,
            message: "Internal server error",
          },
          null
        );
        return;
      }
      if (res.length < 1) {
        // not found User with the username
        result(
          {
            status: 401,
            message: "Incorrect Login Credentials",
          },
          null
        );
        return;
      }

      //found user
      result(null, res[0]);
      return;
    }
  );
};

db.js:

const mysql = require("mysql");

const dbConfig = {
  dev: {
    driver: process.env.DB_DRIVER,
    host: process.env.DB_HOST,
    port: process.env.DB_PORT,
    user: process.env.DB_USER,
    password: process.env.DB_PASSWORD,
    database: process.env.DB_DATABASE,
  },
};

const connection = mysql.createConnection(dbConfig.dev);

connection.connect((error) => {
  if (error) throw error;
  console.log("Successfully connected to the database");
});

module.exports = connection;

What is the correct way to configure an in memory database for testing? and how do I instruct my tests to use the testing database instead of my actual MySQL Database?

Here is an example test:

const app = require('../server');

const supertest = require('supertest');
const request = supertest(app);

describe('testing user registration and login endpoints', () => {
    it('test login without token returns 401', async done => {
        const res = await request.get('/users');
        expect(res.status).toBe(401)
        done();
    });
})