week-7: fix unit tests with pg mock for PostgreSQL integration

app/backend/server.test.js

@@ -1,6 +1,31 @@
 const request = require('supertest');
+
+// Mock the pg Pool before importing app so no real
+// database connection is attempted during tests
+jest.mock('pg', () => {
+  const mPool = {
+    query: jest.fn(),
+  };
+  return { Pool: jest.fn(() => mPool) };
+});
+
+// Mock initDb so the server does not try to create
+// the tasks table on startup during tests
+jest.mock('./db', () => ({
+  pool: {
+    query: jest.fn(),
+  },
+  initDb: jest.fn().mockResolvedValue(),
+}));
+
+const { pool } = require('./db');
 const app = require('./server');
 
+// Reset all mocks between tests so they don't bleed into each other
+beforeEach(() => {
+  jest.clearAllMocks();
+});
+
 describe('Health Check', () => {
   it('GET /api/health returns 200 with status ok', async () => {
     const res = await request(app).get('/api/health');
@@ -11,12 +36,19 @@ describe('Health Check', () => {
 
 describe('Tasks API', () => {
   it('GET /api/tasks returns empty array initially', async () => {
+    pool.query.mockResolvedValueOnce({ rows: [] });
+
     const res = await request(app).get('/api/tasks');
     expect(res.statusCode).toBe(200);
     expect(Array.isArray(res.body)).toBe(true);
+    expect(res.body).toHaveLength(0);
   });
 
   it('POST /api/tasks creates a new task', async () => {
+    pool.query.mockResolvedValueOnce({
+      rows: [{ id: 1, title: 'Test task', completed: false, created_at: new Date() }],
+    });
+
     const res = await request(app)
       .post('/api/tasks')
       .send({ title: 'Test task' });
@@ -31,4 +63,36 @@ describe('Tasks API', () => {
       .send({});
     expect(res.statusCode).toBe(400);
   });
-});
+
+  it('PATCH /api/tasks/:id toggles completed status', async () => {
+    pool.query.mockResolvedValueOnce({
+      rowCount: 1,
+      rows: [{ id: 1, title: 'Test task', completed: true, created_at: new Date() }],
+    });
+
+    const res = await request(app).patch('/api/tasks/1');
+    expect(res.statusCode).toBe(200);
+    expect(res.body.completed).toBe(true);
+  });
+
+  it('PATCH /api/tasks/:id returns 404 when task not found', async () => {
+    pool.query.mockResolvedValueOnce({ rowCount: 0, rows: [] });
+
+    const res = await request(app).patch('/api/tasks/999');
+    expect(res.statusCode).toBe(404);
+  });
+
+  it('DELETE /api/tasks/:id deletes a task', async () => {
+    pool.query.mockResolvedValueOnce({ rowCount: 1 });
+
+    const res = await request(app).delete('/api/tasks/1');
+    expect(res.statusCode).toBe(204);
+  });
+
+  it('DELETE /api/tasks/:id returns 404 when task not found', async () => {
+    pool.query.mockResolvedValueOnce({ rowCount: 0 });
+
+    const res = await request(app).delete('/api/tasks/999');
+    expect(res.statusCode).toBe(404);
+  });
+});