test(mongodb): verify User schema behaviors under connection state 3 (disconnecting) (Variation 3) (JhaSourav07#2006)

## Description

Fixes JhaSourav07#1418

Added test coverage for MongoDB connection state `3` (`disconnecting`)
in `lib/mongodb.test.ts` and `models/User.test.ts` to ensure the
connection flow and User model remain usable during disconnecting state.

## Pillar

* [ ] 🎨 Pillar 1 — New Theme Design
* [ ] 📐 Pillar 2 — Geometric SVG Improvement
* [ ] 🕐 Pillar 3 — Timezone Logic Optimization
* [x] 🛠️ Other (Bug fix, refactoring, docs)

## Visual Preview

Test verification for MongoDB connection state 3 (disconnecting):

<img width="831" height="171" alt="Test Results"
src="https://github.com/user-attachments/assets/183168ff-a4e0-4c1f-9f54-83b77c75a70c"
/>

## Checklist before requesting a review:

* [x] I have read the `CONTRIBUTING.md` file.
* [x] I have tested these changes locally.
* [x] I have run `npm run format` and `npm run lint` locally and
resolved all errors.
* [x] I have updated `README.md` if I added a new theme or URL
parameter.
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standard.
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Author: JhaSourav07

lib/mongodb.test.ts

@@ -113,6 +113,34 @@ describe('dbConnect', () => {
     expect(global.mongoose.promise).toBeNull();
   });
 
+  it('handles mongoose Connection State 3 (disconnecting) gracefully', async () => {
+    process.env.MONGODB_URI = 'mongodb://localhost:27017/test';
+    global.mongoose.conn = null;
+    mockMongooseConnection.readyState = 3;
+
+    const mockMongoose = { connection: 'mock' };
+    setConnectedMongoose(mockMongoose as unknown as typeof mongoose);
+
+    const conn = await dbConnect();
+
+    expect(mongoose.connect).toHaveBeenCalledTimes(1);
+    expect(conn).toBe(mockMongoose);
+    expect(global.mongoose.conn).toBe(mockMongoose);
+  });
+
+  it('returns the cached connection immediately when mongoose is already connected', async () => {
+    process.env.MONGODB_URI = 'mongodb://localhost:27017/test';
+
+    const mockMongoose = { connection: 'mock' };
+    global.mongoose.conn = mockMongoose as unknown as typeof mongoose;
+    mockMongooseConnection.readyState = 1;
+
+    const conn = await dbConnect();
+
+    expect(conn).toBe(mockMongoose);
+    expect(mongoose.connect).not.toHaveBeenCalled();
+  });
+
   it('throws when called from the Edge runtime', async () => {
     vi.stubEnv('NEXT_RUNTIME', 'edge');
     process.env.MONGODB_URI = 'mongodb://localhost:27017/test';

models/User.test.ts

@@ -270,6 +270,20 @@ describe('User Model', () => {
       connectSpy.mockRestore();
     });
   });
+
+  describe('Database Connection State 1 Handling', () => {
+    it('keeps the User model usable while mongoose is connected', async (): Promise<void> => {
+      const readyStateSpy = vi
+        .spyOn(mongoose.connection, 'readyState', 'get')
+        .mockReturnValue(1 as unknown as typeof mongoose.connection.readyState);
+
+      expect(mongoose.connection.readyState).toBe(1);
+      expect(User).toBeDefined();
+      expect(User.modelName).toBe('User');
+
+      readyStateSpy.mockRestore();
+    });
+  });
 });
 
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