This repo demonstrates the problem with running vitest in --no-threads mode, using mongoose and mongodb-memory-server.
git clone https://github.com/revosw/vitest-mms-repro.gitpnpm ipnpm exec vitest --no-threads run
The problem arises when there are two tests importing the same model.
FAIL test1.test.ts [ test1.test.ts ]
OverwriteModelError: Cannot overwrite `user` model once compiled.
❯ Mongoose.model node_modules/.pnpm/[email protected]/node_modules/mongoose/lib/index.js:563:13
❯ model.ts:22:31
20|
21| // Create the User model using the schema
22| export const model = mongoose.model('user', schema);
| ^
23|
❯ test1.test.ts:1:31
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Test Files 1 failed | 1 passed (2)
Tests 1 passed (1)
Start at 23:50:08
Duration 2.13s (transform 30ms, setup 450ms, collect 20ms, tests 1.36s, environment 0ms, prepare 124ms)
Running the same tests without --no-threads works fine.