Unexpected behaviour of `beforeEach` outside of suite without test isolation

What is the problem this feature will solve?

In test runners such as jest or vitest, callbacks passed to the methods before, after, beforeEach or afterEach not wrapped in any describe, are called only when tests in their module are about to start or end. That's also the current behaviour when --test-isolation=process. Unfortunately, when the --test-isolation is none, the callbacks we pass to those 4 functions are added as global callbacks and they start to be called before/after each test in any file.

That's unexpected behaviour and it makes it more difficult to migrate from other test runners to node test runner or from the default --test-isolation=process.

What is the feature you are proposing to solve the problem?

Each module should be wrapped in a suite by default, so the callbacks don't leak to the other test modules. The only exception should be callbacks that we pass to those 4 methods in the global setup file(or its imports I guess).

まず、Node.js のテストランナーが --test-isolation=process と --test-isolation=none の下で before、after、beforeEach、afterEach のコールバックをどのように処理するかを追跡します。グローバルセットアップとその import を含め、個別のテストモジュール間で既存の動作を確認します。モジュールレベルのコールバックが他のモジュールのテストに対して実行されなくなり、グローバルセットアップのコールバックが意図されたスコープを維持すれば完了です。