What are common API test cases you would write?

1. Functional Test Cases

• Verify API returns correct response for valid request
• Test all HTTP methods (GET, POST, PUT, DELETE, PATCH)
• Validate response status codes
• Verify response body structure and data
• Test with different input combinations
• Validate response headers

2. Negative Test Cases

• Test with invalid API endpoint
• Test with invalid HTTP method
• Test with missing required parameters
• Test with invalid data types
• Test with out-of-range values
• Test with special characters and SQL injection
• Test with empty/null values

3. Authentication & Authorization

• Test without authentication token
• Test with invalid/expired token
• Test with valid token
• Test role-based access control
• Test token refresh mechanism

4. Performance Test Cases

• Verify response time is within acceptable limits
• Test API under load (concurrent users)
• Test with large payload
• Verify API handles timeout scenarios

5. Data Validation

• Validate JSON/XML schema
• Verify data types in response
• Check for required vs optional fields
• Validate date formats
• Verify enum values

Example Test Case

Test Case: Create User API

• Endpoint: POST /api/users
• Headers: Content-Type: application/json, Authorization: Bearer token
• Body: {“name”: “John”, “email”: “john@test.com”}
• Expected: Status 201, Response contains user ID
• Validation: User created in database