概述
pytest_assertrepr_compare 是pytest框架中的一个钩子函数，它在比较操作（如 ==, !=, <, >, <=, >=）失败时被触发，用于在比较操作失败时提供自定义的错误报告。这个钩子允许我们提供自定义的错误报告，替换默认的错误信息，以便在断言失败时提供更丰富的调试信息，这样可以在断言失败时生成更具可读性和详细的错误信息，从而帮助调试和定位问题。
使用场景
-
增强错误报告：在断言失败时提供详细和有用的错误信息，帮助更快定位问题。
-
自定义比较逻辑：为特定类型或自定义对象提供定制的比较逻辑和相应的错误报告。
-
易于调试：通过提供更可读的错误信息，减少调试时间，提高效率。
参数
def pytest_assertrepr_compare(config, op, left, right):
# config: pytest 的配置对象，包含有关当前测试会话的所有信息
# op: 比较操作符，表示比较的类型（如 '==', '!=', '<', '>', '<=', '>='）
# left: 比较操作符左侧的值
# right: 比较操作符右侧的值
pass
-
config：pytest的配置对象，包含有关当前测试会话的所有信息。 -
op：比较操作符，表示比较的类型（如 ‘==’, ‘!=’, ‘<’, ‘>’, ‘<=’, ‘>=’）。 -
left：比较操作符左侧的值。 -
right：比较操作符右侧的值。
示例代码
案例一：增强错误报告
目标：在断言失败时提供详细和有用的错误信息，帮助更快定位问题。
步骤：
-
使用
pytest_assertrepr_compare钩子函数。 -
在钩子函数中插入自定义的错误报告逻辑。
示例代码：
# conftest.py
import pytest
def pytest_assertrepr_compare(config, op, left, right):
if op == "==":
return [
"Comparing two values:",
f" value 1: {left}",
f" value 2: {right}",
"Equality assertion failed!",
]
# 示例测试文件 `tests/test_example.py`
def test_example():
assert 2 + 2 == 5
注释：
-
在
pytest_assertrepr_compare钩子函数中，提供断言失败时的自定义错误信息，包括被比较的两个值和相应的比较操作符。 -
测试用例中引入一个故意的错误，以演示自定义错误报告的效果。
案例二：自定义对象的比较
目标：为特定类型或自定义对象提供定制的比较逻辑和相应的错误报告。
步骤：
-
定义一个自定义对象类型。
-
使用
pytest_assertrepr_compare钩子函数，为该类型提供定制的比较逻辑和错误报告。
示例代码：
# conftest.py
import pytest
class CustomObject:
def __init__(self, name, value):
self.name = name
self.value = value
def pytest_assertrepr_compare(config, op, left, right):
if isinstance(left, CustomObject) and isinstance(right, CustomObject) and op == "==":
return [
"Comparing two CustomObject instances:",
f" object 1: {left.name} with value {left.value}",
f" object 2: {right.name} with value {right.value}",
"Equality assertion failed!",
]
# 示例测试文件 `tests/test_example.py`
from conftest import CustomObject
def test_custom_object_comparison():
obj1 = CustomObject("obj1", 100)
obj2 = CustomObject("obj2", 100)
assert obj1 == obj2
注释：
-
定义一个
CustomObject类，并在pytest_assertrepr_compare钩子函数中为该类型的实例提供自定义的比较逻辑和错误报告。 -
在测试用例中比较两个
CustomObject实例，并故意引发断言失败以演示自定义错误报告。
案例三：对列表和字典的比较
目标：在断言列表或字典相等性失败时，提供更具可读性的错误报告，显示详细的差异信息。
步骤：
-
使用
pytest_assertrepr_compare钩子函数。 -
在钩子函数中插入列表和字典的详细比较逻辑。
示例代码：
# conftest.py
import pytest
def pytest_assertrepr_compare(config, op, left, right):
if isinstance(left, list) and isinstance(right, list) and op == "==":
return [
"Comparing two lists:",
f" list 1: {left}",
f" list 2: {right}",
"List equality assertion failed!",
"Differences:",
] + [f" Index {i}: {l} != {r}" for i, (l, r) in enumerate(zip(left, right)) if l != r]
if isinstance(left, dict) and isinstance(right, dict) and op == "==":
return [
"Comparing two dictionaries:",
f" dict 1: {left}",
f" dict 2: {right}",
"Dictionary equality assertion failed!",
"Differences:",
] + [f" Key {key}: {left.get(key)} != {right.get(key)}" for key in set(left.keys()).union(right.keys()) if left.get(key) != right.get(key)]
# 示例测试文件 `tests/test_example.py`
def test_list_comparison():
assert [1, 2, 3] == [1, 3, 2]
def test_dict_comparison():
assert {"a": 1, "b": 2} == {"a": 2, "b": 2}
注释：
-
在
pytest_assertrepr_compare钩子函数中，提供对列表和字典的详细比较逻辑和错误报告。 -
在测试用例中比较两个列表和两个字典，并故意引发断言失败以演示自定义错误报告。
运行和验证
确保目录结构如下：
在项目根目录下运行以下命令：
pytest -s -v --cache-clear
验证输出信息
根据具体的案例，控制台输出应包含自定义的错误报告，显示详细的比较信息和相应的差异。
控制台输出示例
案例一：增强错误报告
______________ test_example ________________
root@Gavin:~/test/hook# pytest -s -v --cache-clear
================================================================================================================== test session starts ==================================================================================================================
platform linux -- Python 3.11.6, pytest-8.0.2, pluggy-1.5.0 -- /usr/bin/python3
cachedir: .pytest_cache
Test order randomisation NOT enabled. Enable with --random-order or --random-order-bucket=<bucket_type>
sensitiveurl: .*
metadata: {'Python': '3.11.6', 'Platform': 'Linux-6.5.0-35-generic-x86_64-with-glibc2.38', 'Packages': {'pytest': '8.0.2', 'pluggy': '1.5.0'}, 'Plugins': {'cov': '4.1.0', 'order': '1.2.0', 'random-order': '1.1.1', 'tornasync': '0.6.0.post2', 'check': '2.2.2', 'instafail': '0.5.0', 'allure-pytest': '2.13.2', 'asyncio': '0.23.6', 'selenium': '4.1.0', 'xdist': '3.5.0', 'variables': '3.1.0', 'rerunfailures': '13.0', 'html': '4.1.1', 'progress': '1.2.5', 'metadata': '3.0.0', 'twisted': '1.14.1', 'picked': '0.5.0', 'anyio': '4.3.0', 'Faker': '24.0.0', 'trio': '0.8.0', 'repeat': '0.9.3', 'base-url': '2.1.0', 'dependency': '0.6.0', 'dotenv': '0.5.2', 'timeout': '2.2.0'}, 'JAVA_HOME': '/usr/lib/jdk1.8.0_171', 'Base URL': '', 'Driver': None, 'Capabilities': {}}
rootdir: /root/test/hook
plugins: cov-4.1.0, order-1.2.0, random-order-1.1.1, tornasync-0.6.0.post2, check-2.2.2, instafail-0.5.0, allure-pytest-2.13.2, asyncio-0.23.6, selenium-4.1.0, xdist-3.5.0, variables-3.1.0, rerunfailures-13.0, html-4.1.1, progress-1.2.5, metadata-3.0.0, twisted-1.14.1, picked-0.5.0, anyio-4.3.0, Faker-24.0.0, trio-0.8.0, repeat-0.9.3, base-url-2.1.0, dependency-0.6.0, dotenv-0.5.2, timeout-2.2.0
asyncio: mode=Mode.STRICT
collected 1 item
tests/test_example.py::test_example FAILED
======================================================================================================================= FAILURES ========================================================================================================================
_____________________________________________________________________________________________________________________ test_example ______________________________________________________________________________________________________________________
def test_example():
> assert 2 + 2 == 5
E assert Comparing two values:
E value 1: 4
E value 2: 5
E Equality assertion failed!
tests/test_example.py:2: AssertionError
================================================================================================================ short test summary info ================================================================================================================
FAILED tests/test_example.py::test_example - assert Comparing two values:
=================================================================================================================== 1 failed in 0.10s ===================================================================================================================
root@Gavin:~/test/hook#
案例二：自定义对象的比较
root@Gavin:~/test/hook# pytest -s -v --cache-clear
================================================================================================================== test session starts ==================================================================================================================
platform linux -- Python 3.11.6, pytest-8.0.2, pluggy-1.5.0 -- /usr/bin/python3
cachedir: .pytest_cache
Test order randomisation NOT enabled. Enable with --random-order or --random-order-bucket=<bucket_type>
sensitiveurl: .*
metadata: {'Python': '3.11.6', 'Platform': 'Linux-6.5.0-35-generic-x86_64-with-glibc2.38', 'Packages': {'pytest': '8.0.2', 'pluggy': '1.5.0'}, 'Plugins': {'cov': '4.1.0', 'order': '1.2.0', 'random-order': '1.1.1', 'tornasync': '0.6.0.post2', 'check': '2.2.2', 'instafail': '0.5.0', 'allure-pytest': '2.13.2', 'asyncio': '0.23.6', 'selenium': '4.1.0', 'xdist': '3.5.0', 'variables': '3.1.0', 'rerunfailures': '13.0', 'html': '4.1.1', 'progress': '1.2.5', 'metadata': '3.0.0', 'twisted': '1.14.1', 'picked': '0.5.0', 'anyio': '4.3.0', 'Faker': '24.0.0', 'trio': '0.8.0', 'repeat': '0.9.3', 'base-url': '2.1.0', 'dependency': '0.6.0', 'dotenv': '0.5.2', 'timeout': '2.2.0'}, 'JAVA_HOME': '/usr/lib/jdk1.8.0_171', 'Base URL': '', 'Driver': None, 'Capabilities': {}}
rootdir: /root/test/hook
plugins: cov-4.1.0, order-1.2.0, random-order-1.1.1, tornasync-0.6.0.post2, check-2.2.2, instafail-0.5.0, allure-pytest-2.13.2, asyncio-0.23.6, selenium-4.1.0, xdist-3.5.0, variables-3.1.0, rerunfailures-13.0, html-4.1.1, progress-1.2.5, metadata-3.0.0, twisted-1.14.1, picked-0.5.0, anyio-4.3.0, Faker-24.0.0, trio-0.8.0, repeat-0.9.3, base-url-2.1.0, dependency-0.6.0, dotenv-0.5.2, timeout-2.2.0
asyncio: mode=Mode.STRICT
collected 1 item
tests/test_example.py::test_custom_object_comparison FAILED
======================================================================================================================= FAILURES ========================================================================================================================
_____________________________________________________________________________________________________________ test_custom_object_comparison _____________________________________________________________________________________________________________
def test_custom_object_comparison():
obj1 = CustomObject("obj1", 100)
obj2 = CustomObject("obj2", 100)
> assert obj1 == obj2
E assert Comparing two CustomObject instances:
E object 1: obj1 with value 100
E object 2: obj2 with value 100
E Equality assertion failed!
tests/test_example.py:6: AssertionError
================================================================================================================ short test summary info ================================================================================================================
FAILED tests/test_example.py::test_custom_object_comparison - assert Comparing two CustomObject instances:
=================================================================================================================== 1 failed in 0.10s ===================================================================================================================
root@Gavin:~/test/hook#
案例三：对列表和字典的比较
root@Gavin:~/test/hook# pytest -s -v --cache-clear
================================================================================================================== test session starts ==================================================================================================================
platform linux -- Python 3.11.6, pytest-8.0.2, pluggy-1.5.0 -- /usr/bin/python3
cachedir: .pytest_cache
Test order randomisation NOT enabled. Enable with --random-order or --random-order-bucket=<bucket_type>
sensitiveurl: .*
metadata: {'Python': '3.11.6', 'Platform': 'Linux-6.5.0-35-generic-x86_64-with-glibc2.38', 'Packages': {'pytest': '8.0.2', 'pluggy': '1.5.0'}, 'Plugins': {'cov': '4.1.0', 'order': '1.2.0', 'random-order': '1.1.1', 'tornasync': '0.6.0.post2', 'check': '2.2.2', 'instafail': '0.5.0', 'allure-pytest': '2.13.2', 'asyncio': '0.23.6', 'selenium': '4.1.0', 'xdist': '3.5.0', 'variables': '3.1.0', 'rerunfailures': '13.0', 'html': '4.1.1', 'progress': '1.2.5', 'metadata': '3.0.0', 'twisted': '1.14.1', 'picked': '0.5.0', 'anyio': '4.3.0', 'Faker': '24.0.0', 'trio': '0.8.0', 'repeat': '0.9.3', 'base-url': '2.1.0', 'dependency': '0.6.0', 'dotenv': '0.5.2', 'timeout': '2.2.0'}, 'JAVA_HOME': '/usr/lib/jdk1.8.0_171', 'Base URL': '', 'Driver': None, 'Capabilities': {}}
rootdir: /root/test/hook
plugins: cov-4.1.0, order-1.2.0, random-order-1.1.1, tornasync-0.6.0.post2, check-2.2.2, instafail-0.5.0, allure-pytest-2.13.2, asyncio-0.23.6, selenium-4.1.0, xdist-3.5.0, variables-3.1.0, rerunfailures-13.0, html-4.1.1, progress-1.2.5, metadata-3.0.0, twisted-1.14.1, picked-0.5.0, anyio-4.3.0, Faker-24.0.0, trio-0.8.0, repeat-0.9.3, base-url-2.1.0, dependency-0.6.0, dotenv-0.5.2, timeout-2.2.0
asyncio: mode=Mode.STRICT
collected 2 items
tests/test_example.py::test_list_comparison FAILED
tests/test_example.py::test_dict_comparison FAILED
======================================================================================================================= FAILURES ========================================================================================================================
_________________________________________________________________________________________________________________ test_list_comparison __________________________________________________________________________________________________________________
def test_list_comparison():
> assert [1, 2, 3] == [1, 3, 2]
E assert Comparing two lists:
E list 1: [1, 2, 3]
E list 2: [1, 3, 2]
E List equality assertion failed!
E Differences:
E Index 1: 2 != 3
E Index 2: 3 != 2
tests/test_example.py:2: AssertionError
_________________________________________________________________________________________________________________ test_dict_comparison __________________________________________________________________________________________________________________
def test_dict_comparison():
> assert {"a": 1, "b": 2} == {"a": 2, "b": 2}
E AssertionError: assert Comparing two dictionaries:
E dict 1: {'a': 1, 'b': 2}
E dict 2: {'a': 2, 'b': 2}
E Dictionary equality assertion failed!
E Differences:
E Key a: 1 != 2
tests/test_example.py:5: AssertionError
================================================================================================================ short test summary info ================================================================================================================
FAILED tests/test_example.py::test_list_comparison - assert Comparing two lists:
FAILED tests/test_example.py::test_dict_comparison - AssertionError: assert Comparing two dictionaries:
=================================================================================================================== 2 failed in 0.11s ===================================================================================================================
root@Gavin:~/test/hook#
总结
通过 pytest_assertrepr_compare 钩子，我们可以在比较操作失败时提供自定义的错误报告，从而增强错误信息的可读性和可调试性。本文详细介绍了钩子的使用场景、参数及具体案例，并提供了完整的示例代码和详细解释，帮助读者更好地理解和应用这个钩子函数。
