api-testing

SKILL.md

API Testing

Expert knowledge for testing HTTP APIs with Supertest (TypeScript/JavaScript) and httpx/pytest (Python).

TypeScript/JavaScript (Supertest)

Installation

# Using Bun
bun add -d supertest @types/supertest

# or: npm install -D supertest @types/supertest

Basic Setup
import { describe, it, expect } from 'vitest'
import request from 'supertest'
import { app } from './app'

describe('API Tests', () => {
  it('returns health status', async () => {
    const response = await request(app)
      .get('/api/health')
      .expect(200)

    expect(response.body).toEqual({ status: 'ok' })
  })

  it('creates a user', async () => {
    const response = await request(app)
      .post('/api/users')
      .send({ name: 'John Doe', email: 'john@example.com' })
      .expect(201)

    expect(response.body).toMatchObject({
      id: expect.any(Number),
      name: 'John Doe',
    })
  })

  it('validates required fields', async () => {
    await request(app)
      .post('/api/users')
      .send({ name: 'John Doe' })
      .expect(400)
  })
})

Request Methods

// GET
await request(app).get('/api/users').expect(200)

// POST with body
await request(app)
  .post('/api/users')
  .send({ name: 'John' })
  .expect(201)

// PUT
await request(app)
  .put('/api/users/1')
  .send({ name: 'Jane' })
  .expect(200)

// DELETE
await request(app).delete('/api/users/1').expect(204)

Headers and Query Parameters

// Set headers
await request(app)
  .get('/api/protected')
  .set('Authorization', 'Bearer token123')
  .expect(200)

// Query parameters
await request(app)
  .get('/api/users')
  .query({ page: 1, limit: 10 })
  .expect(200)

Authentication Testing

describe('Authentication', () => {
  let authToken: string

  beforeAll(async () => {
    const response = await request(app)
      .post('/api/auth/login')
      .send({ email: 'user@example.com', password: 'password123' })
      .expect(200)

    authToken = response.body.token
  })

  it('accesses protected endpoint', async () => {
    await request(app)
      .get('/api/protected')
      .set('Authorization', `Bearer ${authToken}`)
      .expect(200)
  })

  it('rejects without token', async () => {
    await request(app).get('/api/protected').expect(401)
  })
})

Error Handling

it('handles validation errors', async () => {
  const response = await request(app)
    .post('/api/users')
    .send({ email: 'invalid-email' })
    .expect(400)

  expect(response.body).toMatchObject({
    error: 'Validation failed',
    details: expect.any(Array),
  })
})

it('handles not found', async () => {
  await request(app).get('/api/users/999999').expect(404)
})

Python (httpx + pytest)

Installation

uv add --dev httpx pytest-asyncio

Basic Setup

import pytest
from fastapi.testclient import TestClient
from main import app

client = TestClient(app)

def test_health_check():
    response = client.get("/api/health")
    assert response.status_code == 200
    assert response.json() == {"status": "ok"}

def test_create_user():
    response = client.post(
        "/api/users",
        json={"name": "John Doe", "email": "john@example.com"}
    )
    assert response.status_code == 201
    data = response.json()
    assert data["name"] == "John Doe"
    assert "id" in data

def test_not_found():
    response = client.get("/api/users/999")
    assert response.status_code == 404

Fixtures

@pytest.fixture
def auth_token(client):
    response = client.post(
        "/api/auth/login",
        json={"email": "user@example.com", "password": "password123"}
    )
    return response.json()["token"]

def test_protected_endpoint(client, auth_token):
    response = client.get(
        "/api/protected",
        headers={"Authorization": f"Bearer {auth_token}"}
    )
    assert response.status_code == 200

File Upload

def test_file_upload(client, tmp_path):
    test_file = tmp_path / "test.txt"
    test_file.write_text("test content")

    with open(test_file, "rb") as f:
        response = client.post(
            "/api/upload",
            files={"file": ("test.txt", f, "text/plain")}
        )

    assert response.status_code == 200

GraphQL Testing

it('queries GraphQL endpoint', async () => {
  const query = `
    query GetUser($id: ID!) {
      user(id: $id) { id name email }
    }
  `

  const response = await request(app)
    .post('/graphql')
    .send({ query, variables: { id: '1' } })
    .expect(200)

  expect(response.body.data.user).toMatchObject({
    id: '1',
    name: expect.any(String),
  })
})

Performance Testing

it('responds within acceptable time', async () => {
  const start = Date.now()
  await request(app).get('/api/users').expect(200)
  const duration = Date.now() - start
  expect(duration).toBeLessThan(100) // 100ms threshold
})

Best Practices

Group related endpoints in describe blocks

Reset database between tests

Validate status codes first

Check response structure

Test error message format

Mock external services

Test both happy path and error cases

See Also

vitest-testing - Unit testing framework

playwright-testing - E2E API testing

test-quality-analysis - Test quality patterns