vitest useFakeTimers causes the postgres connection to hang

[rxliuli]

I encountered an issue while using vitest for unit testing. When I use vitest's useFakeTimers simultaneously, postgres queries hang indefinitely until they time out. However, pg (node-postgres) does not have this problem. I'm not sure what is happening; I discovered this issue while testing Cloudflare Workers.

Describe the bug

If vi.useFakeTimers() is removed, the query can be performed normally and results are returned.

 FAIL  test/index.test.ts > useFakeTimers
Error: Test timed out in 5000ms.
If this is a long-running test, pass a timeout value as the last argument or configure it globally with "testTimeout".

Reproduction

1. Start a local Postgres service

docker run --name vitest-postgres -e POSTGRES_PASSWORD=pass -p 5432:5432 -d postgres

2. Create a test file

import { it, vi } from 'vitest'
import postgres from 'postgres'

it('useFakeTimers', async () => {
  vi.useFakeTimers()
  const sql = postgres(
    'postgres://postgres:pass@localhost:5432/postgres?sslmode=disable',
    {
      max: 5,
      fetch_types: false,
    },
  )
  const r = await sql`select 1`
  console.log(r)
  vi.useRealTimers()
})

3. pnpm vitest index.test.ts

System Info

System:
    OS: macOS 15.5
    CPU: (12) arm64 Apple M2 Max
    Memory: 441.38 MB / 64.00 GB
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 22.14.0 - /usr/local/bin/node
    npm: 10.9.2 - /usr/local/bin/npm
    pnpm: 10.5.2 - /usr/local/bin/pnpm
    bun: 1.1.6 - ~/.bun/bin/bun
  Browsers:
    Brave Browser: 131.1.73.105
    Chrome: 138.0.7204.101
    Edge: 128.0.2739.54
    Safari: 18.5

The following code using pg will not be affected by useFakeTimers.

import { it, vi } from 'vitest'
import { Client } from 'pg'

it('useFakeTimers & pg', async () => {
  vi.useFakeTimers()
  const client = new Client(
    'postgres://postgres:pass@localhost:5432/postgres?sslmode=disable',
  )
  await client.connect()
  const r = await client.query('select 1')
  console.log(r)
  await client.end()
  vi.useRealTimers()
})

Related issues
vitest-dev/vitest#8302