Encapsulating Assertion Logic in Pytest for API Automation Testing

In API automation testing, assertions verify that the response meets expectations; encapsulating these assertions enhances code readability and maintainability while reducing duplication.

1. Basic concept – Python’s assert statement can be used directly, for example:

response = requests.get("https://api.example.com")
assert response.status_code == 200, "接口请求失败"

2. Encapsulated status‑code assertion

def assert_status_code(response, expected_status_code=200):
    """Validate that the HTTP status code matches the expected value."""
    assert response.status_code == expected_status_code, f"状态码不匹配。预期：{expected_status_code}，实际：{response.status_code}"

3. Encapsulated JSON data assertion

import jsonpath

def assert_json(response, jsonpath_expr, expected_value):
    """Validate that a JSON field extracted by a JSONPath expression matches the expected value."""
    actual_value = jsonpath.jsonpath(response.json(), jsonpath_expr)
    assert actual_value[0] == expected_value, f"JSON 数据不匹配。预期：{expected_value}，实际：{actual_value[0]}"

4. Encapsulated database assertion

import pymysql

def assert_db(query, expected_result):
    """Validate that the result of a SQL query matches the expected result."""
    conn = pymysql.connect(host='localhost', user='root', password='password', db='testdb')
    cursor = conn.cursor()
    cursor.execute(query)
    result = cursor.fetchone()
    cursor.close()
    conn.close()
    assert result == expected_result, f"数据库查询结果不匹配。预期：{expected_result}，实际：{result}"

5. Generic assertion class

class ApiAssert:
    @staticmethod
    def assert_status_code(response, expected_status_code=200):
        assert response.status_code == expected_status_code, f"状态码不匹配。预期：{expected_status_code}，实际：{response.status_code}"

    @staticmethod
    def assert_json(response, jsonpath_expr, expected_value):
        actual_value = jsonpath.jsonpath(response.json(), jsonpath_expr)
        assert actual_value[0] == expected_value, f"JSON 数据不匹配。预期：{expected_value}，实际：{actual_value[0]}"

    @staticmethod
    def assert_db(query, expected_result):
        conn = pymysql.connect(host='localhost', user='root', password='password', db='testdb')
        cursor = conn.cursor()
        cursor.execute(query)
        result = cursor.fetchone()
        cursor.close()
        conn.close()
        assert result == expected_result, f"数据库查询结果不匹配。预期：{expected_result}，实际：{result}"

6. Using the encapsulated assertion class in a test case

def test_api():
    response = requests.get("https://api.example.com")
    ApiAssert.assert_status_code(response, 200)
    ApiAssert.assert_json(response, "$.status", "success")
    ApiAssert.assert_db("SELECT * FROM users WHERE id=1", (1, "John Doe"))

By wrapping assertion logic into reusable functions and a class, developers can write cleaner, more maintainable API tests, improving overall testing efficiency.