Tests using different environments should always be isolated

[AriPerkkio]

Describe the bug

• Ref: feat!: support running tests using VM context #3203 (comment)

When threads are enabled and there are multiple test environments used by the test cases, there should be no multiple test environments used in a single thread. Instead the test cases should be grouped by environment and run in separate threads.

It's already intended in code but it's not working:

vitest/packages/vitest/src/node/pools/threads.ts

Lines 165 to 166 in fbb56ad

	// always run environments isolated between each other
	for (const env of envs) {

Reproduction

https://stackblitz.com/edit/vitest-dev-vitest-ihs847?file=vite.config.ts

import { defineConfig } from 'vitest/config';

export default defineConfig({
  test: {
    singleThread: true,
    isolate: false,
  },
});

/**
 * @vitest-environment jsdom
 */

import { test, expect } from 'vitest';

test('Node globals not found', async () => {
  globalThis.__leaking_from_jsdom = 'leaking';
  expect(globalThis.__leaking_from_node).toBe(undefined);
});

/**
 * @vitest-environment node
 */

import { test, expect } from 'vitest';

test('jsdom globals not found', async () => {
  globalThis.__leaking_from_node = 'leaking';
  expect(globalThis.__leaking_from_jsdom).toBe(undefined);
});

System Info

Stackblitz

Used Package Manager

npm

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• vitest-dev-vitest-ihs847 (Open reproduction)