Add task title validation for POST /tasks

sample-app/src/app.test.ts

@@ -1,4 +1,4 @@
-import { describe, it, expect } from 'vitest';
+import { describe, expect, it } from 'vitest';
 import request from 'supertest';
 import { createApp } from './app.js';
 
@@ -23,6 +23,36 @@ describe('Task API', () => {
     expect(list.body).toHaveLength(1);
   });
 
+  it('trims surrounding whitespace from task titles', async () => {
+    const app = createApp();
+
+    const created = await request(app).post('/tasks').send({ title: '  Trim me  ' });
+    expect(created.status).toBe(201);
+    expect(created.body.title).toBe('Trim me');
+
+    const list = await request(app).get('/tasks');
+    expect(list.status).toBe(200);
+    expect(list.body).toHaveLength(1);
+    expect(list.body[0].title).toBe('Trim me');
+  });
+
+  it.each([
+    { body: {}, expectedMessage: 'Title must be a non-empty string' },
+    { body: { title: '' }, expectedMessage: 'Title must be a non-empty string' },
+    { body: { title: '   ' }, expectedMessage: 'Title must be a non-empty string' },
+    { body: { title: 42 }, expectedMessage: 'Title must be a non-empty string' },
+  ])('rejects invalid task titles: $body', async ({ body, expectedMessage }) => {
+    const app = createApp();
+
+    const res = await request(app).post('/tasks').send(body);
+    const list = await request(app).get('/tasks');
+
+    expect(res.status).toBe(400);
+    expect(res.body).toEqual({ error: expectedMessage });
+    expect(list.status).toBe(200);
+    expect(list.body).toEqual([]);
+  });
+
   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

@@ -1,5 +1,6 @@
 import { Router } from 'express';
 import type { TaskStore } from './store.js';
+import { TASK_TITLE_ERROR, normalizeTaskTitle } from './validation.js';
 
 export function createTaskRouter(store: TaskStore): Router {
   const router = Router();
@@ -10,11 +11,17 @@ 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);
+    try {
+      const title = normalizeTaskTitle(req.body?.title);
+      const task = store.create(title);
+      return res.status(201).json(task);
+    } catch (error) {
+      if (error instanceof Error && error.message === TASK_TITLE_ERROR) {
+        return res.status(400).json({ error: error.message });
+      }
+
+      throw error;
+    }
   });
 
   router.get('/:id', (req, res) => {

sample-app/src/tasks/store.test.ts

@@ -1,5 +1,6 @@
 import { describe, it, expect } from 'vitest';
 import { TaskStore } from './store.js';
+import { TASK_TITLE_ERROR } from './validation.js';
 
 describe('TaskStore', () => {
   it('creates a task with sensible defaults', () => {
@@ -12,6 +13,19 @@ describe('TaskStore', () => {
     expect(task.createdAt).toBe(task.updatedAt);
   });
 
+  it('trims surrounding whitespace from task titles', () => {
+    const store = new TaskStore();
+    const task = store.create('  Write the talk  ');
+
+    expect(task.title).toBe('Write the talk');
+  });
+
+  it('rejects blank task titles', () => {
+    const store = new TaskStore();
+
+    expect(() => store.create('   ')).toThrow(TASK_TITLE_ERROR);
+  });
+
   it('lists every created task', () => {
     const store = new TaskStore();
     store.create('a');

sample-app/src/tasks/store.ts

@@ -1,5 +1,6 @@
 import { randomUUID } from 'node:crypto';
 import type { Task } from './types.js';
+import { normalizeTaskTitle } from './validation.js';
 
 /**
  * In-memory task store. Intentionally small so it is easy to reason about
@@ -18,10 +19,11 @@ export class TaskStore {
   }
 
   create(title: string): Task {
+    const normalizedTitle = normalizeTaskTitle(title);
     const now = new Date().toISOString();
     const task: Task = {
       id: randomUUID(),
-      title,
+      title: normalizedTitle,
       completed: false,
       createdAt: now,
       updatedAt: now,

sample-app/src/tasks/validation.ts

@@ -0,0 +1,9 @@
+export const TASK_TITLE_ERROR = 'Title must be a non-empty string';
+
+export function normalizeTaskTitle(title: unknown): string {
+  if (typeof title !== 'string' || title.trim().length === 0) {
+    throw new Error(TASK_TITLE_ERROR);
+  }
+
+  return title.trim();
+}