Validate task titles on create

sample-app/src/app.test.ts

@@ -12,17 +12,36 @@ describe('Task API', () => {
 
   it('creates and then lists a task', async () => {
     const app = createApp();
-
+ 
     const created = await request(app).post('/tasks').send({ title: 'Demo task' });
     expect(created.status).toBe(201);
     expect(created.body.title).toBe('Demo task');
     expect(created.body.completed).toBe(false);
-
+ 
     const list = await request(app).get('/tasks');
     expect(list.status).toBe(200);
     expect(list.body).toHaveLength(1);
   });
-
+
+  it.each([
+    { name: 'missing title', payload: {} },
+    { name: 'empty title', payload: { title: '' } },
+    { name: 'whitespace-only title', payload: { title: '   ' } },
+    { name: 'non-string title', payload: { title: 42 } },
+  ])('rejects invalid title payload: $name', async ({ payload }) => {
+    const app = createApp();
+
+    const before = await request(app).get('/tasks');
+    expect(before.body).toHaveLength(0);
+
+    const res = await request(app).post('/tasks').send(payload);
+    expect(res.status).toBe(400);
+    expect(res.body).toEqual({ error: 'Title must be a non-empty string' });
+
+    const after = await request(app).get('/tasks');
+    expect(after.body).toHaveLength(0);
+  });
+
   it('marks a task completed via PATCH', async () => {
     const app = createApp();
     const created = await request(app).post('/tasks').send({ title: 'Finish slides' });

sample-app/src/tasks/routes.ts

@@ -10,11 +10,19 @@ export function createTaskRouter(store: TaskStore): Router {
   });
 
   router.post('/', (req, res) => {
-    // Exercise 1: validate that req.body.title is a non-empty string and
-    // return 400 with a helpful message when it is not.
     const { title } = req.body ?? {};
-    const task = store.create(title);
-    res.status(201).json(task);
+
+    if (typeof title !== 'string') {
+      return res.status(400).json({ error: 'Title must be a non-empty string' });
+    }
+
+    const trimmedTitle = title.trim();
+    if (trimmedTitle.length === 0) {
+      return res.status(400).json({ error: 'Title must be a non-empty string' });
+    }
+
+    const task = store.create(trimmedTitle);
+    return res.status(201).json(task);
   });
 
   router.get('/:id', (req, res) => {