Testing with external services in PyTest

Introduction

We test with external services to check if our code works well when it talks to other programs or websites.

When your app needs to get data from a website or API.

When you want to check if your code handles responses from a payment service.

When your program sends emails through an external email service.

When you want to make sure your app works with a database or cloud service.

When you want to test how your code behaves if the external service is slow or down.

Syntax

PyTest

import pytest
import requests
from unittest.mock import patch

@patch('requests.get')
def test_external_service(mock_get):
    mock_get.return_value.status_code = 200
    mock_get.return_value.json.return_value = {'key': 'value'}

    response = requests.get('https://api.example.com/data')
    assert response.status_code == 200
    assert response.json() == {'key': 'value'}

Use @patch to replace the real external call with a fake one during tests.

This helps tests run fast and not depend on the real service being available.

Examples

This example mocks a POST request to an external service and checks the response code.

PyTest

from unittest.mock import patch

@patch('requests.post')
def test_post_service(mock_post):
    mock_post.return_value.status_code = 201
    response = requests.post('https://api.example.com/create')
    assert response.status_code == 201

This test calls the real service but is skipped if the service is not available.

PyTest

import pytest
import requests

@pytest.mark.skip(reason='External service not available')
def test_real_service_call():
    response = requests.get('https://api.example.com/data')
    assert response.status_code == 200

Sample Program

This test replaces the real HTTP GET call with a fake one that returns a fixed response. It then checks if the code correctly handles that response.

PyTest

import pytest
import requests
from unittest.mock import patch

@patch('requests.get')
def test_fetch_data(mock_get):
    # Setup mock response
    mock_get.return_value.status_code = 200
    mock_get.return_value.json.return_value = {'name': 'Test User', 'id': 123}

    # Call the function that uses requests.get
    response = requests.get('https://api.example.com/user')

    # Check the response
    assert response.status_code == 200
    assert response.json() == {'name': 'Test User', 'id': 123}

Important Notes

Always mock external services in tests to avoid slow or unreliable tests.

Use unittest.mock.patch to replace external calls with fake responses.

Test how your code handles errors like timeouts or bad responses from external services.

Summary

Testing with external services means faking those services during tests.

This makes tests faster and more reliable.

Use mocking tools like patch to do this easily.