How do I overwrite environment variables dynamically in a typical node environment?

[on3iro]

Hey folks,

I am currently in the process of migration from jest to vitest in one of my projects.
I had a hack inside my old setup configuration, that is now coming to bite me again, as it is no longer working with vitest.
I generally assume, that there must be a better way to do what I want, so I really hope someone can shine some light on this:

As far as I can tell most nodejs server applications are typically structured in a way, that they instantiate their database connection inside a plain file, export the connection and import it inside their controllers etc. Take for example this simplified db file:

export const db = pgp({
  host: process.env.POSTGRES_HOST ?? 'db',
  port:
    process.env.NODE_ENV === 'test'
      ? parseInt(process.env.POSTGRES_PORT ?? '5432')
      : 5432,
  database: process.env.POSTGRES_DB,
  user: process.env.POSTGRES_USER,
  password: process.env.POSTGRES_PASSWORD,
  max: 30,
})

Now I would typically import the database inside my controllers like this:

import { db } from 'db'
router.post('/', { /* some config */}, () => {
   const result = await db.query('somequery');
})

This is all fine, but there is one major flaw I can't seem to overcome, when it comes to testing.
I use some setup helpers for my tests, like this:

export async function setupEnvironment(): Promise<IntegrationEnvironment> {
  dbContainer = await new GenericContainer('postgres:14.2-alpine')
    .withEnvironment({
      POSTGRES_PASSWORD: POSTGRES_TEST_PASSWORD,
      POSTGRES_USER: POSTGRES_TEST_USER,
      POSTGRES_DB: POSTGRES_TEST_DB,
    })
    .withExposedPorts(POSTGRES_TESTING_HOST_PORT)
    .start()

  const dbPort = dbContainer.getMappedPort(POSTGRES_TESTING_HOST_PORT)

  await runMigrations(dbPort)

  process.env['VERSION'] = 'testing'
  process.env['POSTGRES_HOST'] = dbContainer.getHost()
  process.env['POSTGRES_PORT'] = `${dbPort}`
  process.env['POSTGRES_DB'] = POSTGRES_TEST_DB
  process.env['POSTGRES_USER'] = POSTGRES_TEST_USER
  process.env['POSTGRES_PASSWORD'] = POSTGRES_TEST_PASSWORD

  // Note the require here
  const { server } = require('server/server')
  appServer = server

 // NOTE the require here
  const { db, PostgresBgioStore } = require('server/db')

  const servers = await server.run(0)

  return {
    dbContainer,
    servers,
    db,
    PostgresBgioStore,
  }
}

As you can see there are two require()-statements in there - these are the afformentioned hack, that does no longer work with vitest and where I assume there is a better solution.
So what does the hack do:
As you can see above my database connection is set by environment variables for port etc., because it runs in various different docker setups and environments.
The issue is, that we instantiate the database eagerly, this means that as soon as the file is imported/required during a test, the environment variables are applied. Because of this we don't have access to the testcontainer specific information at the right time.
The inline require() kinda solved this, by delaying the import of the respective file to a point in time, where we already know the port etc. of the testcontainer.
Vitest does not support this, however.

I was also thinking of finding a way to explicitely instantiated the database at a specific point in time and wire it with my server + routers. But I would then probably have to write a middleware doing so (I am using a koa server) and all the examples of typical koa/expressjs apps I've found typically don't seem to do this. Which is why I assume I am fundamentally misunderstanding something here.

Any idea how I could fix this or what would be a good approach here?

Thanks in advance!

[on3iro]

I think I've found a way:

I declare the db with let and use a closure which is called at a specific time and only then binds the actual database objects to the exported variables. This seems to work fine, as far as I can tell.
Still it would be nice to know, if there is some kind of best practices for things like this in the node world :)