Vitest >=1.0.0-beta.5 config.base browser test error demo

Using Vitest 1.0.0-beta.5 or later (including v1.0.1) when vite.config.js defines base produces the following error when running browser tests:

TypeError: Failed to fetch dynamically imported module: http://localhost:5173/@id/vitest/utils
This error originated in "demo.test.js" test file. It doesn't mean the error was thrown inside the file itself, but while it was running.

This demo repo helped me determine the root cause:

• vitejs/vite#5657: fix!: return 404 for resources requests outside the base path made Vite reject URLs outside of config.base.
• This change became part of Vite 5.0.0-beta.8
• Vitest's dependency on Vite was bumped to ^5.0.0-beta.15 as part of vitest-dev/vitest#4368: chore!: update vite@5 and rollup@4
• This change became part of Vitest 1.0.0-beta.5

This issue was filed just before I got the chance, so I'll attach my info there:

• vitest-dev/vitest: unhandled error with browser tests and modified base #4686

Reproduction steps

These are distilled from the steps recorded in the commit messages of this repo.

Initial setup for last good combination

Clone all these repos in the same directory:

git clone https://github.com/mbland/vitest-utils-browser-import.git
git clone https://github.com/vitejs/vite.git
git clone https://github.com/vitest-dev/vitest.git

Restore Vite and Vitest to the last versions that worked together without producing this error:

cd vite
git reset --hard v5.0.0-beta.7

# Not needed the first time, but for each rebuild:
rm -rf node_modules packages/*/node_modules

pnpm i --ignore-scripts --frozen-lockfile
pnpm build

cd ../vitest
git reset --hard v1.0.0-beta.4

# Same as above:
rm -rf node_modules packages/*/node_modules

pnpm i --ignore-scripts --frozen-lockfile
pnpm build

cd ../vitest-utils-browser-import
pnpm i --ignore-scripts
pnpm test

This should allow the Vitest UI to run and for the test (which does nothing but return null) to pass.

Setup failure with Vite commit

To reproduce the error, follow the same steps as above for the first Vite build:

cd ../vite
git reset --hard 40fd2d9bf4073420e6c334f48dc3b63558b688ce
rm -rf node_modules packages/*/node_modules
pnpm i --ignore-scripts --frozen-lockfile
pnpm build

cd ../vitest-utils-browser-import
pnpm i --ignore-scripts
pnpm test

This should produce the same failure as above.

Workaround

The workaround is to delete the config.base value in vitest.config.js. A version of this is already encoded here:

pnpm test:workaround