generate-jest-tests

name	generate-jest-tests
description	Generates a Jest test suite for backend API endpoints and controllers. Use when asked to generate unit tests, integration tests, API tests, or a Jest test suite for backend code.

Skill — Generate Jest Tests

What You Do

Read the backend code and produce a comprehensive Jest test suite covering API endpoints and business logic.

Steps

1. Read the [BACKEND] GitHub Issue — understand what was built
2. Read src/backend/routes/ — identify all endpoints
3. Read src/backend/controllers/ — understand business logic
4. Read docs/design/design-doc.md — confirm API contracts
5. Generate test files in src/backend/__tests__/
6. Generate Prisma mock in src/backend/__tests__/__mocks__/prisma.ts
7. Raise PR with all test files

Test File Structure

// Feature: {feature name}
// Source: GitHub Issue #{number}

import request from 'supertest'
import app from '../index'

describe('{Feature} API', () => {

  let authToken: string

  beforeAll(async () => {
    const res = await request(app)
      .post('/api/auth/login')
      .send({ email: '[e-mail]', password: 'password123' })
    authToken = res.body.token
  })

  describe('{METHOD} /api/{path}', () => {
    it('should return {status} on success', async () => {
      // arrange — set up test data
      // act — make the request
      // assert — verify response
    })

    it('should return 401 without auth token', async () => {})
    it('should return 400 if required fields missing', async () => {})
  })

})

Coverage Requirements

Every endpoint must have at minimum:

Test Type	What It Verifies
Happy path	Correct input returns correct status and response shape
Auth test	No token returns 401
Validation	Missing required fields returns 400
Edge case	At least one edge case per endpoint

Prisma Mock Setup

Always generate this mock file for unit tests:

// src/backend/__tests__/__mocks__/prisma.ts
import { PrismaClient } from '@prisma/client'
import { mockDeep, mockReset, DeepMockProxy } from 'jest-mock-extended'

export const prismaMock = mockDeep<PrismaClient>()

beforeEach(() => {
  mockReset(prismaMock)
})

Testing Patterns

Arrange / Act / Assert — always use this pattern

it('should add item to cart', async () => {
  // arrange
  const payload = { menuItemId: 1, quantity: 1 }

  // act
  const res = await request(app)
    .post('/api/cart/items')
    .set('Authorization', `Bearer ${authToken}`)
    .send(payload)

  // assert
  expect(res.status).toBe(201)
  expect(res.body).toHaveProperty('id')
  expect(res.body.menuItemId).toBe(1)
})

Response shape validation — always check shape not just status

// CORRECT
expect(res.body).toHaveProperty('items')
expect(res.body.items).toBeInstanceOf(Array)

// WRONG — only checking status is not enough
expect(res.status).toBe(200)

Edge Cases to Always Test

For any cart-like feature check:

• Add same item twice → quantity increments not duplicates
• Remove item not in cart → 404
• Get empty cart → returns empty items array not error
• Update quantity to 0 → 400 or removes item

For any auth-protected feature check:

• Expired token → 401
• Malformed token → 401
• Missing Authorization header → 401

Example Test File (Cart API)

describe('Cart API', () => {
  describe('POST /api/cart/items', () => {
    it('should add item and return 201', async () => {})
    it('should return 401 without token', async () => {})
    it('should return 400 if menuItemId missing', async () => {})
    it('should increment quantity if item already in cart', async () => {})
  })

  describe('DELETE /api/cart/items/:id', () => {
    it('should remove item and return 200', async () => {})
    it('should return 401 without token', async () => {})
    it('should return 404 if item not in cart', async () => {})
  })
})