doc: fix module syncBuiltinESMExports example

Fix failing code and add explanations of each assert.

PR-URL: #34284
Reviewed-By: Guy Bedford <guybedford@gmail.com>
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>

doc/api/module.md

@@ -87,21 +87,29 @@ does not add or remove exported names from the [ES Modules][].
 
 ```js
 const fs = require('fs');
+const assert = require('assert');
 const { syncBuiltinESMExports } = require('module');
 
-fs.readFile = null;
+fs.readFile = newAPI;
 
 delete fs.readFileSync;
 
-fs.newAPI = function newAPI() {
+function newAPI() {
   // ...
-};
+}
+
+fs.newAPI = newAPI;
 
 syncBuiltinESMExports();
 
 import('fs').then((esmFS) => {
-  assert.strictEqual(esmFS.readFile, null);
-  assert.strictEqual('readFileSync' in fs, true);
+  // It syncs the existing readFile property with the new value
+  assert.strictEqual(esmFS.readFile, newAPI);
+  // readFileSync has been deleted from the required fs
+  assert.strictEqual('readFileSync' in fs, false);
+  // syncBuiltinESMExports() does not remove readFileSync from esmFS
+  assert.strictEqual('readFileSync' in esmFS, true);
+  // syncBuiltinESMExports() does not add names
   assert.strictEqual(esmFS.newAPI, undefined);
 });
 ```