Testing with Testcontainers

Testcontainers 328,662 starts a throwaway Docker 514 container per test run and stops it afterwards. For MongoDB 1,815 that is @testcontainers/mongodb (github.com/testcontainers/testcontainers-node (https://github.com/testcontainers/testcontainers-node 2,617 ), MIT, version 12.1.0). You pin the exact server image your cluster runs, and the same tool covers everything else the suite touches — Redis 2,763 , S3, an SMTP sink.

import { MongoDBContainer } from '@testcontainers/mongodb';
export async function startDatabase() {
  container = await new MongoDBContainer('mongo:8.3').start();
  // the module runs mongod with --replSet and initiates it, so transactions work
  await mongoose.connect(container.getConnectionString(), { directConnection: true });
}
export const stopDatabase = async () => {
  await mongoose.disconnect(); await container.stop();
};

directConnection: true is required: the container advertises a replica-set host name that does not resolve from the host machine, and without the flag topology discovery times out. That listing is configuration only — the machine used here has Docker CLI 29.6.2 but no running daemon, so this suite was not executed; every other listing in Seeding and Testing was.

Use the memory server for the suite that runs on every save, and Testcontainers where a test must exercise the exact server build or several services at once. Both hide behind the same two functions, so switching is one import.