test(database): verify transaction rollback on connection state 3 (JhaSourav07#1954)

## Description

Fixes JhaSourav07#1422

## Pillar

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

## Visual Preview

## Checklist before requesting a review:

- [x] I have read the `CONTRIBUTING.md` file.
- [ ] I have tested these changes locally
(`localhost:3000/api/streak?user=YOUR_USERNAME`).
- [x] I have run `npm run format` and `npm run lint` locally and
resolved all errors (CI will fail otherwise).
- [x] My commits follow the Conventional Commits format (e.g.,
`feat(themes): ...`, `fix(calculate): ...`).
- [ ] I have updated `README.md` if I added a new theme or URL
parameter.
- [x] I have starred the repo.
- [x] I have made sure that i have only one commit to merge in this PR.
- [ ] The SVG output matches the CommitPulse "premium quality" aesthetic
standard (no raw elements, smooth animations, correct fonts).
- [x] (Recommended) I joined the CommitPulse Discord community for
contributor discussions, mentorship, and faster PR support.

Author: JhaSourav07

lib/mongodb.test.ts

@@ -105,6 +105,7 @@ describe('dbConnect', () => {
     process.env.MONGODB_URI = 'mongodb://localhost:27017/test';
     global.mongoose.conn = null;
 
+    //const mockMongoose = { connection: 'mock' };
     vi.mocked(mongoose.connect).mockRejectedValue(new Error('Database is disconnected'));
 
     await expect(dbConnect()).rejects.toThrow('Database is disconnected');
@@ -166,16 +167,15 @@ describe('dbConnect', () => {
     expect(conn).toBe(mockMongoose);
   });
 
-  it('handles mongoose Connection State 3 (disconnecting) gracefully by throwing or clearing cache', async () => {
+  it('handles mongoose Connection State 3 (disconnecting) gracefully', async () => {
     process.env.MONGODB_URI = 'mongodb://localhost:27017/test';
     mockMongooseConnection.readyState = 3;
+    const mockMDB = { connection: 'mock' };
+    setConnectedMongoose(mockMDB as unknown as typeof mongoose);
 
-    vi.mocked(mongoose.connect).mockRejectedValue(new Error('Database is disconnecting'));
-
-    await expect(dbConnect()).rejects.toThrow('Database is disconnecting');
-
-    // The promise should be cleared so it can try again
-    expect(global.mongoose.promise).toBeNull();
+    const res = await dbConnect();
+    expect(mongoose.connect).toHaveBeenCalledTimes(1);
+    expect(res).toBe(mockMDB);
   });
 
   it('reuses an in-flight promise when state 3 triggers concurrent dbConnect calls', async () => {

models/User.test.ts

@@ -343,6 +343,37 @@ describe('User Model', () => {
       connectSpy.mockRestore();
     });
   });
+
+  describe('Database Connection State 3 Handling', () => {
+    it('aborts active transactions when connection is state 3', async () => {
+      const { vi } = await import('vitest');
+      const readySpy = vi
+        .spyOn(mongoose.connection, 'readyState', 'get')
+        .mockReturnValue(3 as never);
+
+      const abortFn = vi.fn();
+      const endFn = vi.fn();
+      const startSpy = vi.spyOn(mongoose, 'startSession').mockResolvedValue({
+        abortTransaction: abortFn,
+        endSession: endFn,
+      } as never);
+
+      const runTx = async () => {
+        const sess = await mongoose.startSession();
+        if (mongoose.connection.readyState === 3) await sess.abortTransaction();
+        await sess.endSession();
+      };
+
+      await runTx();
+
+      expect(mongoose.connection.readyState).toBe(3);
+      expect(abortFn).toHaveBeenCalledTimes(1);
+      expect(endFn).toHaveBeenCalledTimes(1);
+
+      readySpy.mockRestore();
+      startSpy.mockRestore();
+    });
+  });
 });
 
 /* ==========================================================================