How to run Next.js and Jest concurrently, with an instance of Next.js already running?

[codigoisaac]

Summary

I have this script in my Next.js project, where I start a Next.js server (because the tests need it) and run Jest tests using concurrently:

"test": "npm run services:up && 
    npm run services:wait:database && 
    concurrently --names next,jest 
        --kill-others --success command-jest 
        'next dev' 'jest --runInBand --verbose'"

It was working fine until i updated Next.js to version 16. In previous versions, it was possible to have multiple Next.js instances running on the same project, but in Next.js 16 it isn't anymore.

Because of this, when I have my development server running and run this test command above, Next.js exits with code 1 because it can't start a second instance, and because of the --kill-others flag, concurrently will kill the Jest process and the tests will not finish.

If I don't use the --kill-others flag, and Next.js successfully starts because there is no other instance running, it will stay running forever.

I would need one of this solutions, or others:

1. Start the Next.js instance only if one ins't already running,
2. Be able to run two Next.js instances at the same time,
3. Inform concurrently that if Next.js fails specifically because another instance already exist, it's fine and other processes should continue, or
4. Inform concurrently that upon succeeding on the jest command, all other commands and its processes should be terminated - then I would remove --kill-others flag and depend solely upon Jest return.

However, I don't know how to do any of those solutions, or if there would be a better one.

Additional information

No response

Example

No response

[icyJoseph]

Maybe you need to set this to false for testing:

• next.js/packages/next/src/server/config-shared.ts

  Lines 828 to 839 in c450169

  	/**
  	* Acquires a lockfile at `<distDir>/lock` when starting `next dev` or `next
  	* build`. Failing to acquire the lock causes the process to exit with an
  	* error message.
  	*
  	* This is because if multiple processes write to the same `distDir` at the
  	* same time, it can mangle the state of the directory. Disabling this option
  	* is not recommended.
  	*
  	* @default true
  	*/
  	lockDistDir?: boolean

module.exports = {
  experimental: {
     lockDistDir: false
  }
}

[codigoisaac]

How could I do that?
AFAIK this option is not available for next.config.js.

[icyJoseph]

I linked the config-shared file, which lists all the options for next.config.js

import type { NextConfig } from "next";

const nextConfig: NextConfig = {
  cacheComponents: true,
  experimental: {
    lockDistDir: false,
  },
};

export default nextConfig;

[codigoisaac]

Thank you @icyJoseph 👊
I ended up changing my testing approach, because this was going to a strange path, so I didn't tested this and can't say if that works. But thanks for your help, man. Really appreciated.