fix: should run restore in the current event loop (#172)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

- **Refactor**
- Improved performance of the `restore` method by executing tasks in
parallel.

- **Tests**
- Enhanced test suite with refined import statements, better assertion
methods, and a new test case for asynchronous behavior.
- Introduced a `sleep` function for testing asynchronous code execution.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

index.js

@@ -22,8 +22,7 @@ module.exports.default = mock;
 Object.assign(mock, mm, {
   async restore() {
     cluster.restore();
-    await mockAgent.restore();
-    return await mm.restore();
+    await Promise.all([ mockAgent.restore(), mm.restore() ]);
   },
 
   /**

test/mock_env.test.js

@@ -1,12 +1,10 @@
-'use strict';
-
-const path = require('path');
-const assert = require('assert');
+const path = require('node:path');
+const { strict: assert } = require('node:assert');
 const mm = require('..');
+
 const fixtures = path.join(__dirname, 'fixtures');
 
 describe('test/mock_env.test.js', () => {
-
   let app;
   before(() => {
     app = mm.app({
@@ -17,9 +15,33 @@ describe('test/mock_env.test.js', () => {
   after(() => app.close());
   afterEach(mm.restore);
 
-  it('should mock env succes', () => {
+  it('should mock env success', () => {
     app.mockEnv('prod');
-    assert(app.config.env === 'prod');
-    assert(app.config.serverEnv === 'prod');
+    assert.equal(app.config.env, 'prod');
+    assert.equal(app.config.serverEnv, 'prod');
+  });
+
+  it('should keep mm.restore execute in the current event loop', async () => {
+    mm.restore();
+    assert.equal(app.config.env, 'unittest');
+    assert.equal(app.config.serverEnv, undefined);
+
+    app.mockEnv('prod');
+    assert.equal(app.config.env, 'prod');
+    assert.equal(app.config.serverEnv, 'prod');
+
+    await sleep(1);
+    assert.equal(app.config.env, 'prod');
+    assert.equal(app.config.serverEnv, 'prod');
+
+    mm.restore();
+    assert.equal(app.config.env, 'unittest');
+    assert.equal(app.config.serverEnv, undefined);
   });
 });
+
+function sleep(ms) {
+  return new Promise(resolve => {
+    setTimeout(resolve, ms);
+  });
+}