How to Encapsulate and Call Mock Services in pytest

Install pytest using pip; unittest.mock is part of the Python standard library.

Create the module to test, e.g., my_module.py with a fetch_data function that uses requests.get to retrieve JSON data and raises HTTPError on failure.

Create a test file test_my_module.py.

Import pytest, unittest.mock's MagicMock and patch, and fetch_data from my_module.

Define a fixture mock_requests_get that patches requests.get and yields the mock object.

Create a helper function setup_mock_response(mock_get, status_code=200, json_data=None) that configures the mock to return a MagicMock response with the given status code and JSON data, and simulates HTTPError for status codes >=400.

Write test cases: test_fetch_data_success sets up a mock response with status 200 and JSON data, calls fetch_data, asserts the returned value matches the data, and verifies that mock_requests_get was called once with the expected URL.

Write test_fetch_data_failure that sets up a mock response with status 404, calls fetch_data inside a pytest.raises context for HTTPError, and asserts the mock was called correctly.

Run the tests with the command pytest test_my_module.py.

Explanation: patch temporarily replaces requests.get with a mock; MagicMock records calls and allows setting return values and side effects; setup_mock_response simplifies configuring mock responses; assert_called_once_with verifies the mock was invoked with the correct arguments.

# my_module.py
import requests

def fetch_data(url):
    """
    从给定的 URL 获取数据。
    参数:
        url (str): API 端点的 URL。
    返回:
        dict: API 返回的 JSON 数据。
    异常:
        requests.exceptions.HTTPError: 如果 HTTP 请求失败。
    """
    response = requests.get(url)
    response.raise_for_status()  # 如果 HTTP 请求失败，抛出异常
    return response.json()

# test_my_module.py
import pytest
from unittest.mock import MagicMock, patch
from my_module import fetch_data

@pytest.fixture
def mock_requests_get():
    """
    使用 pytest 的 fixture 来模拟 requests.get 方法。
    返回:
        MagicMock: 模拟的 requests.get 对象。
    """
    with patch('requests.get') as mock_get:
        yield mock_get

def setup_mock_response(mock_get, status_code=200, json_data=None):
    """
    设置 mock 响应。
    参数:
        mock_get (MagicMock): 模拟的 requests.get 对象。
        status_code (int): 响应的状态码，默认为 200。
        json_data (dict): 响应的 JSON 数据，默认为 None。
    """
    mock_response = MagicMock()
    mock_response.status_code = status_code  # 设置状态码
    if json_data is not None:
        mock_response.json.return_value = json_data  # 设置 JSON 响应数据
    if status_code >= 400:
        mock_response.raise_for_status.side_effect = requests.exceptions.HTTPError("请求失败")  # 设置异常
    # 设置 mock_get 的返回值为模拟的响应对象
    mock_get.return_value = mock_response

def test_fetch_data_success(mock_requests_get):
    """
    测试 fetch_data 函数在成功情况下的行为。
    """
    setup_mock_response(mock_requests_get, status_code=200, json_data={"key": "value"})
    result = fetch_data("http://example.com/api/data")
    assert result == {"key": "value"}
    mock_requests_get.assert_called_once_with("http://example.com/api/data")

def test_fetch_data_failure(mock_requests_get):
    """
    测试 fetch_data 函数在失败情况下的行为。
    """
    setup_mock_response(mock_requests_get, status_code=404)
    with pytest.raises(requests.exceptions.HTTPError):
        fetch_data("http://example.com/api/data")
    mock_requests_get.assert_called_once_with("http://example.com/api/data")