API client testing in PyTest - Build an Automation Script

Verify GET /users API returns correct user data

Preconditions (2)

Step 1: Send a GET request to http://api.example.com/users/1

Step 2: Check the HTTP status code of the response

Step 3: Check the response body contains user data with ID 1 and name 'John Doe'

✅ Expected Result: Response status code is 200 and response body JSON contains {'id': 1, 'name': 'John Doe'}

Automation Requirements - pytest

Assertions Needed:

Assert response status code is 200

Assert response JSON contains correct user ID and name

Best Practices:

Use requests library for HTTP calls

Use pytest fixtures for setup if needed

Keep tests independent and repeatable

Use clear and descriptive assertion messages

Automated Solution

PyTest

import requests
import pytest

BASE_URL = "http://api.example.com"


def test_get_user_by_id():
    user_id = 1
    expected_name = "John Doe"
    response = requests.get(f"{BASE_URL}/users/{user_id}")
    
    # Assert status code is 200
    assert response.status_code == 200, f"Expected status code 200 but got {response.status_code}"
    
    data = response.json()
    
    # Assert user ID and name in response
    assert data.get('id') == user_id, f"Expected user id {user_id} but got {data.get('id')}"
    assert data.get('name') == expected_name, f"Expected user name '{expected_name}' but got '{data.get('name')}'"

This test sends a GET request to the API endpoint for user with ID 1.

We check the HTTP status code to confirm the request succeeded (200 means OK).

Then we parse the JSON response and verify the user ID and name match expected values.

Assertions include clear messages to help understand failures.

Using requests library is standard for HTTP calls in Python.

This test is simple, independent, and repeatable.

Common Mistakes - 3 Pitfalls

Not checking the HTTP status code before parsing JSON

Hardcoding full URLs multiple times

Not providing assertion messages

Bonus Challenge

Now add data-driven testing to verify multiple user IDs and names

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