What is API testing?

API testing validates a service at the HTTP interface level:

• requests and responses
• status codes and headers
• payload correctness (JSON shape)
• authentication/authorization
• error handling and rate limits

What to test (checklist)

• Status codes: 200/201/204, 400/401/403/404, 429, 5xx
• Response body: required keys, value types, constraints
• Contracts: backwards compatibility
• Auth: missing token, invalid token, role permissions
• Idempotency: repeated requests behave correctly
• Performance: basic response time budgets

Diagram: test levels around an API

  graph TD
A[Unit tests\n(request builders, validators)] --> B[API tests\n(HTTP-level)]
B --> C[End-to-end tests\n(user workflows)]

Tip

• Write API tests as deterministic as possible.
• Avoid relying on external services in CI.

🧪 Try It Yourself

Exercise 1 – Write a unittest TestCase

Exercise 2 – assertRaises

Exercise 3 – setUp and tearDown