Storybook Vitest much slower on CI compared to Test Runner

[Spence1115]

Summary

I've been trying to migrate our monorepo to Vitest for storybook instead of the test runner, but so far it seems far slower than the test runner was. The docs don't suggest so, but should I be building the storybook in advance or anything like that?

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[dosubot[bot]]

You don't need to build Storybook in advance for Vitest tests on CI—the standard approach is to run Vitest directly, just like you would locally, and the official docs and example CI configs don't include a Storybook build step for this workflow (docs).

Slower performance with Vitest on CI is usually due to async rendering and the need for explicit waits in your tests. Unlike the legacy test runner, Vitest doesn't have a built-in global DOM readiness hook, so you need to use async Testing Library queries (like findBy...), wrap assertions in waitFor, and use waitForElementToBeRemoved as needed in your play functions or tests. This ensures your tests are robust and don't race against rendering or asset loading, which can be slower or more variable in CI (discussion).

Other common causes of slowdowns include complex or duplicated Vite/Vitest config, plugin duplication, or lack of caching. For best results, make sure your Vite config is merged properly (especially if you have multiple Vitest projects), avoid duplicating plugins, and keep your coverage include/exclude patterns consistent. If you have a complex setup, isolating test config in a separate vitest.config.ts and manually merging Vite config in .storybook/main.ts can help (issue).

If you want to optimize further, check your CI resource allocation and consider using Vitest's parallelization and caching features. But fundamentally, robust async handling in your tests is the most important factor for reliable and performant CI runs with Storybook + Vitest.

To reply, just mention @dosu.

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