All Connections connect before app is Served

I have an application that has connects to Redis, Mongo, and Elasticsearch but how can I make sure all the connections are connected before the app is served? I notice that Elasticsearch usually takes longer and when I test my app using Supertest that the database connects but the console.info('Successfully connected to db'); doesn't log to the console before the tests start to run.

server.ts

const client = redis.createClient({ host: process.env.REDIS })


client.on('connect', function () {
    console.log('Redis client connected');
});

mongoose
      .connect(dbURL)
      .then(() => {
        return console.info(`Successfully connected to ${db}`);
      })
      .catch(error => {
        console.error('Error connecting to database: ', error);
        return process.exit(1);
      });
  };
const app = express();
export default app;

main.ts

import server from './server'
server.listen(8000)