fix(runtime): reapply test.env before every file in a reused worker

[methakon]

fix(runtime): reapply test.env before every file in a reused worker

Under isolate: false a worker is reused across test files, but config.env
is merged into process.env only once, when the worker is spawned:

• packages/vitest/src/node/pool.ts builds the worker env from
  ...ctx.config.env, ...project.config.env
• packages/vitest/src/node/config/serializeConfig.ts serializes
  env: { ...viteConfig?.env, ...config.env }

Nothing reapplies those keys per file, so a file that assigns to one of them
leaks its value into every later file in the same worker. Vitest 4 reapplied
test.env before each file; 5.0.3 does not, and the 5.0 migration guide does
not mention the change.

Reproduction

8 files, isolate: false, maxWorkers: 1 so they share a worker. Each file
reads DATABASE_URL at module scope and the first one overwrites it:

// f01.test.ts
const seenOnEntry = process.env.DATABASE_URL
process.env.DATABASE_URL = 'postgres://h/private-01'
it('f01 starts with the configured test.env value', () => {
  expect(seenOnEntry).toBe('postgres://h/shared')
})

On 5.0.3: 6 failed | 2 passed (8). With this change: 8 passed (8).

The fix

runBaseTests.run now calls applyConfigEnv(config.env) inside the per-file
loop.

The placement matters. With isolate: false and maxWorkers: 1,
groupSpecs (packages/vitest/src/node/pool.ts) explicitly batches every file
into a single run request, so a reapplication placed in the per-run setup would
never fire between files.

applyConfigEnv only restores keys the config actually declares. Keys the
config does not mention still leak between files, which is the documented
behaviour of isolate: false and is unchanged — there is a test pinning that.

Values are stringified the same way the spawn-time merge does, because Vite's
own keys (PROD, DEV, SSR) reach config.env as booleans and assigning a
boolean to process.env does not yield '1' / ''.

Tests

test/e2e/test/isolate-false-reapplies-env.test.ts:

• both forks and threads, isolate: false, maxWorkers: 1
• each file logs its pid and the test asserts both files shared a worker, so it
  fails loudly instead of silently going vacuous if scheduling changes. With more
  workers the files are split across them, the leak cannot occur, and the test
  would pass with the bug still present.
• a third test pins that unconfigured keys still leak

Without this change the two test.env cases fail and the unconfigured-keys case
still passes. Full unit suite is unchanged: the same 36 spec files fail before
and after, all pre-existing on a clean checkout.

Fixes #11423.

[github-actions]

Your account has been automatically flagged as likely to be created by a bot, LLM, or agent,
and will be automatically closed. If you believe this is a mistake, please reply to this comment and we will review it.

These measures help us reduce maintenance burden and keep the team's work efficient. See our AI contributions policy for more context.

[netlify]

✅ Deploy Preview for vitest-dev ready!

Built without sensitive environment variables

Name	Link
🔨 Latest commit	d8fa218
🔍 Latest deploy log	https://app.netlify.com/projects/vitest-dev/deploys/6abf4f267d55b50008afb009
😎 Deploy Preview	https://deploy-preview-11441--vitest-dev.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.
🤖 Make changes	Run an agent on this branch

---

To edit notification comments on pull requests, go to your Netlify project configuration.