isolate

• Type: boolean
• Default: true
• CLI: --no-isolate, --isolate=false

Run tests in an isolated environment. This option has no effect on vmThreads and vmForks pools.

Browser Mode

In Browser Mode, a page runs its test files one after another in the same document when isolate is false. The browser keeps one instance per module URL for the lifetime of the document, so the files share every module they import, and a module that one file mocked stays mocked for the files that run after it in the same page. Vitest reports an error when a file mocks a module that the page already imported, and when a file imports a module that an earlier file mocked. See Mocking with isolate: false for the patterns that work without isolation.

Disabling this option might improve performance if your code doesn't rely on side effects (which is usually true for projects with node environment).

TIP

You can disable isolation for specific test files by using Vitest workspaces and disabling isolation per project.