Unit testing strategies for API routes

For Next.js App Router API routes with Vitest, test the route handler functions directly:

typescriptCopy
import { describe, it, expect, vi } from 'vitest';
import { GET, POST } from './route';

// Mock Prisma
vi.mock('@/lib/db/prisma', () => ({
  db: {
    conversation: {
      findMany: vi.fn(),
      create: vi.fn(),
    },
  },
}));

describe('GET /api/conversations', () => {
  it('should return conversations list', async () => {
    const mockData = [
      { id: '1', title: 'Test Conv', platform: 'chatgpt' },
    ];

    const { db } = await import('@/lib/db/prisma');
    vi.mocked(db.conversation.findMany).mockResolvedValue(mockData);

    const request = new Request('http://localhost:3000/api/conversations');
    const response = await GET(request);
    const body = await response.json();

    expect(response.status).toBe(200);
    expect(body.data).toEqual(mockData);
  });

  it('should handle errors gracefully', async () => {
    const { db } = await import('@/lib/db/prisma');
    vi.mocked(db.conversation.findMany).mockRejectedValue(
      new Error('DB connection failed')
    );

    const request = new Request('http://localhost:3000/api/conversations');
    const response = await GET(request);

    expect(response.status).toBe(500);
  });
});

Key patterns:

• Import and call route handlers directly (no HTTP server needed)
• Mock database layer with vi.mock
• Use standard Request/Response objects
• Test both happy path and error cases