no-vitest-single-thread-pool-by-default

Disallow single-thread pool defaults in committed Vitest config.

Rule catalog ID: R039

Targeted pattern scope

vitest.config.*
vitest.workspace.*
vite.config.* when Vitest pool options are configured
test.poolOptions.*.(threads|maxThreads|maxWorkers) static values set to 1

What this rule reports

This rule reports single-thread pool defaults such as:

threads: 1
maxThreads: 1
maxWorkers: 1

when they are configured under test.poolOptions.

Why this rule exists

Single-thread pool defaults reduce test throughput and can hide concurrency issues. In shared configuration, these values are often temporary debugging settings that should not be committed.

❌ Incorrect

import { defineConfig } from "vitest/config";

export default defineConfig({
    test: {
        poolOptions: {
            threads: {
                maxThreads: 1,
            },
        },
    },
});

✅ Correct

import { defineConfig } from "vitest/config";

export default defineConfig({
    test: {
        poolOptions: {
            threads: {
                maxThreads: 2,
            },
        },
    },
});

Behavior and migration notes

this rule checks static numeric/string values only
it targets shared config files, not arbitrary source modules

ESLint flat config example

import vite from "@typpi/eslint-plugin-vite";

export default [vite.configs.strict, vite.configs.vitest];

When not to use it

Disable this rule only if your project intentionally enforces single-thread pool execution in committed shared config.

Package documentation

Vitest config reference

Targeted pattern scope​

What this rule reports​

Why this rule exists​

❌ Incorrect​

✅ Correct​

Behavior and migration notes​

ESLint flat config example​

When not to use it​

Package documentation​

Further reading​