configuring-vitest-4

Vitest 4.x multi-project configuration uses defineConfig with a projects array, where each project defines its own pool, environment, and coverage settings. Structure projects as separate objects with explicit include patterns for coverage and environment-specific configurations like browser or node.

maxWorkers controls the total number of worker threads Vitest spawns, while fileParallelism determines how many test files run concurrently within each worker. Adjust both based on your CPU cores and test file count to optimize throughput without resource exhaustion.

Coverage include patterns in Vitest 4.x are defined in the coverage object within defineConfig or per-project settings. Specify file globs like src/**/*.ts to explicitly include source files for coverage reporting, filtering out test files and node_modules automatically.

Yes, Vitest 4.x projects support per-project environment settings. Define environment: 'browser' or environment: 'node' within each project object to run different suites in their respective environments with isolated configurations and dependencies.

server.deps in Vitest 4.x controls how Vite pre-processes and caches dependencies during test runs. Configure it to optimize import resolution, inline certain packages, or exclude others from optimization, improving test startup and iteration speed.