diff --git a/apps/backend/src/__tests__/profiles.test.ts b/apps/backend/src/__tests__/profiles.test.ts
index 0633b841..0f61f728 100644
--- a/apps/backend/src/__tests__/profiles.test.ts
+++ b/apps/backend/src/__tests__/profiles.test.ts
@@ -1,10 +1,9 @@
+import { Prisma, type PrismaClient } from '@prisma/client';
 import Fastify, { type FastifyInstance } from 'fastify';
 import { describe, it, expect, beforeEach, vi } from 'vitest';
 
 import { profileRoutes } from '../routes/profiles.js';
 
-import type { PrismaClient } from '@prisma/client';
-
 const mockUser = {
   id: 'user-123',
   email: 'test@example.com',
@@ -22,11 +21,27 @@ const mockUser = {
   providerId: 'gh-123',
 };
 
+const mockUserFindUnique = vi.fn();
+const mockUserFindFirst = vi.fn();
+const mockUserUpdate = vi.fn();
+const mockPlatformLinkAggregate = vi.fn();
+const mockPlatformLinkCreate = vi.fn();
+const mockPlatformLinkFindFirst = vi.fn();
+const mockPlatformLinkUpdate = vi.fn();
+const mockPlatformLinkDelete = vi.fn();
+
 const mockPrisma = {
   user: {
-    findUnique: vi.fn(),
-    findFirst: vi.fn(),
-    update: vi.fn(),
+    findUnique: mockUserFindUnique,
+    findFirst: mockUserFindFirst,
+    update: mockUserUpdate,
+  },
+  platformLink: {
+    aggregate: mockPlatformLinkAggregate,
+    create: mockPlatformLinkCreate,
+    findFirst: mockPlatformLinkFindFirst,
+    update: mockPlatformLinkUpdate,
+    delete: mockPlatformLinkDelete,
   },
 };
 
@@ -45,7 +60,7 @@ describe('GET /api/profiles/me', () => {
   beforeEach(() => vi.clearAllMocks());
 
   it('should return user profile with displayName', async () => {
-    mockPrisma.user.findUnique.mockResolvedValue(mockUser);
+    mockUserFindUnique.mockResolvedValue(mockUser);
     const app = await buildApp();
     const res = await app.inject({ method: 'GET', url: '/api/profiles/me' });
     expect(res.statusCode).toBe(200);
@@ -57,7 +72,7 @@ describe('GET /api/profiles/me', () => {
   });
 
   it('should return 404 if user not found', async () => {
-    mockPrisma.user.findUnique.mockResolvedValue(null);
+    mockUserFindUnique.mockResolvedValue(null);
     const app = await buildApp();
     const res = await app.inject({ method: 'GET', url: '/api/profiles/me' });
     expect(res.statusCode).toBe(404);
@@ -69,8 +84,8 @@ describe('PUT /api/profiles/me', () => {
   beforeEach(() => vi.clearAllMocks());
 
   it('should update profile and return updated data', async () => {
-    mockPrisma.user.findFirst.mockResolvedValue(null);
-    mockPrisma.user.update.mockResolvedValue({ ...mockUser, displayName: 'Updated Name' });
+    mockUserFindFirst.mockResolvedValue(null);
+    mockUserUpdate.mockResolvedValue({ ...mockUser, displayName: 'Updated Name' });
     const app = await buildApp();
     const res = await app.inject({
       method: 'PUT',
@@ -90,10 +105,11 @@ describe('PUT /api/profiles/me', () => {
     });
     expect(res.statusCode).toBe(400);
     expect(res.json().error).toBe('Validation failed');
+    expect(mockUserUpdate).not.toHaveBeenCalled();
   });
 
-  it('should return 409 if username is already taken (pre-check)', async () => {
-    mockPrisma.user.findFirst.mockResolvedValue({ id: 'other-user' });
+  it('should return 409 if username is already taken', async () => {
+    mockUserFindFirst.mockResolvedValue({ id: 'other-user' });
     const app = await buildApp();
     const res = await app.inject({
       method: 'PUT',
@@ -102,14 +118,18 @@ describe('PUT /api/profiles/me', () => {
     });
     expect(res.statusCode).toBe(409);
     expect(res.json().error).toBe('Username already taken');
+    expect(mockUserUpdate).not.toHaveBeenCalled();
   });
 
   it('should return 409 when a concurrent request wins the unique constraint race (P2002)', async () => {
     // Both requests pass the findFirst check; the DB unique constraint fires on
     // the losing write — Prisma raises P2002.
-    mockPrisma.user.findFirst.mockResolvedValue(null);
-    const p2002 = Object.assign(new Error('Unique constraint failed'), { code: 'P2002' });
-    mockPrisma.user.update.mockRejectedValue(p2002);
+    mockUserFindFirst.mockResolvedValue(null);
+    const p2002 = new Prisma.PrismaClientKnownRequestError('Unique constraint failed', {
+      code: 'P2002',
+      clientVersion: 'test',
+    });
+    mockUserUpdate.mockRejectedValue(p2002);
 
     const app = await buildApp();
     const res = await app.inject({
@@ -123,8 +143,8 @@ describe('PUT /api/profiles/me', () => {
   });
 
   it('should return 500 for unexpected database errors during update', async () => {
-    mockPrisma.user.findFirst.mockResolvedValue(null);
-    mockPrisma.user.update.mockRejectedValue(new Error('Connection refused'));
+    mockUserFindFirst.mockResolvedValue(null);
+    mockUserUpdate.mockRejectedValue(new Error('Connection refused'));
 
     const app = await buildApp();
     const res = await app.inject({
@@ -138,7 +158,7 @@ describe('PUT /api/profiles/me', () => {
   });
 
   it('should not call findFirst when no username is provided in the update', async () => {
-    mockPrisma.user.update.mockResolvedValue({ ...mockUser, displayName: 'New Name' });
+    mockUserUpdate.mockResolvedValue({ ...mockUser, displayName: 'New Name' });
     const app = await buildApp();
     const res = await app.inject({
       method: 'PUT',
@@ -147,6 +167,103 @@ describe('PUT /api/profiles/me', () => {
     });
 
     expect(res.statusCode).toBe(200);
-    expect(mockPrisma.user.findFirst).not.toHaveBeenCalled();
+    expect(mockUserFindFirst).not.toHaveBeenCalled();
   });
-});
\ No newline at end of file
+});
+
+describe('Platform link routes', () => {
+  beforeEach(() => vi.clearAllMocks());
+
+  it('should return 400 for invalid link create body', async () => {
+    const app = await buildApp();
+    const res = await app.inject({
+      method: 'POST',
+      url: '/api/profiles/me/links',
+      payload: { platform: '', username: '' },
+    });
+
+    expect(res.statusCode).toBe(400);
+    expect(res.json().error).toBe('Validation failed');
+    expect(mockPlatformLinkCreate).not.toHaveBeenCalled();
+  });
+
+  it('should create a platform link with a valid body', async () => {
+    const createdLink = {
+      id: 'link-123',
+      userId: 'user-123',
+      platform: 'github',
+      username: 'octocat',
+      url: 'https://github.com/octocat',
+      displayOrder: 2,
+    };
+
+    mockPlatformLinkAggregate.mockResolvedValue({ _max: { displayOrder: 1 } });
+    mockPlatformLinkCreate.mockResolvedValue(createdLink);
+
+    const app = await buildApp();
+    const res = await app.inject({
+      method: 'POST',
+      url: '/api/profiles/me/links',
+      payload: { platform: 'github', username: 'octocat' },
+    });
+
+    expect(res.statusCode).toBe(201);
+    expect(res.json()).toEqual(createdLink);
+    expect(mockPlatformLinkAggregate).toHaveBeenCalledWith({
+      where: { userId: 'user-123' },
+      _max: { displayOrder: true },
+    });
+    expect(mockPlatformLinkCreate).toHaveBeenCalledWith({
+      data: {
+        userId: 'user-123',
+        platform: 'github',
+        username: 'octocat',
+        url: expect.stringContaining('octocat'),
+        displayOrder: 2,
+      },
+    });
+  });
+
+  it('should return 404 when updating a link that does not exist', async () => {
+    mockPlatformLinkFindFirst.mockResolvedValue(null);
+
+    const app = await buildApp();
+    const res = await app.inject({
+      method: 'PUT',
+      url: '/api/profiles/me/links/link-404',
+      payload: { platform: 'github', username: 'octocat' },
+    });
+
+    expect(res.statusCode).toBe(404);
+    expect(res.json().error).toBe('Link not found');
+    expect(mockPlatformLinkFindFirst).toHaveBeenCalledWith({
+      where: { id: 'link-404', userId: 'user-123' },
+    });
+    expect(mockPlatformLinkUpdate).not.toHaveBeenCalled();
+  });
+
+  it('should delete an existing platform link', async () => {
+    mockPlatformLinkFindFirst.mockResolvedValue({
+      id: 'link-123',
+      userId: 'user-123',
+      platform: 'github',
+      username: 'octocat',
+      url: 'https://github.com/octocat',
+      displayOrder: 0,
+    });
+    mockPlatformLinkDelete.mockResolvedValue({ id: 'link-123' });
+
+    const app = await buildApp();
+    const res = await app.inject({
+      method: 'DELETE',
+      url: '/api/profiles/me/links/link-123',
+    });
+
+    expect(res.statusCode).toBe(204);
+    expect(res.body).toBe('');
+    expect(mockPlatformLinkFindFirst).toHaveBeenCalledWith({
+      where: { id: 'link-123', userId: 'user-123' },
+    });
+    expect(mockPlatformLinkDelete).toHaveBeenCalledWith({ where: { id: 'link-123' } });
+  });
+});