Vitest fails with react-start in a pnpm workspace monorepo #6246
Description
Which project does this relate to?
Start
Describe the bug
When using TanStack Start with Vitest in a pnpm workspace, tests fail with:
TypeError: Cannot read properties of null (reading 'useState')
This occurs when testing components that are imported from workspace packages that have React as a peer dependency.
Root Cause: The TanStack Start Vite plugin applies optimizeDeps configuration unconditionally, including in the Vitest test environment. This interferes with module resolution, causing React to be resolved as null when importing components from workspace packages.
Impact: This bug affects all pnpm workspace configurations (regardless of hoisting settings), making it impossible to use Vitest for testing TanStack Start applications that import components from local workspace packages. This is a common pattern in monorepo setups.
// This errors:
plugins: [tanstackStart(), viteReact()]// This does not error:
plugins: [
process.env.VITEST !== 'true' && tanstackStart(),
viteReact(),
]Your Example Website or App
https://github.com/onlywei/repro-tanstack-start-vitest
Steps to Reproduce the Bug or Issue
- Clone the repro: https://github.com/onlywei/repro-tanstack-start-vitest
- Run
pnpm install - Run
pnpm test
Expected behavior
Tests should pass without errors. Components imported from workspace packages should be able to use React hooks normally during Vitest test execution.
The TanStack Start plugin should not interfere with Vitest's module resolution. Ideally, the plugin should automatically detect when running in a test environment and skip optimization steps that are not needed for testing.
Screenshots or Videos
No response
Platform
- Router / Start Version: 1.145.0
- OS: MacOS
- Vite Version: 7.3.0
- Vitest version: 4.0.16
Additional context
No response