书籍来源：房荔枝 梁丽丽《pytest框架与自动化测试应用》
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失败时加载PDB环境
在工具栏中会有一个小虫子的图标，一般笔者在调试时使用这个查看变量等的情况。PDB(Python Debugger)是Python内建的调试器，如果习惯使用它也是一个不错的选择。pytest允许通过以下命令在执行失败时进入这个调试器模式，代码如下：
举例说明：
pytest会在测试用例失败（或者Ctrl+C）时，调用这个调试器，可以访问测试用例的本地变量x。失败的信息存储在sys.last_value、sys.last_type、sys.last_traceback变量中，可以在交互环境中访问它们。使用exit命令，即可退出PDB环境。
代码如下：
def test_fail():
x = 1
assert x == 0 执行pytest --pdb test_pdb.py，结果如下：
PS D:\SynologyDrive\CodeLearning\WIN\pytest-book\src\chapter-2> pytest --pdb .\test_pdb.py
========================================================================================================= test session starts =========================================================================================================
platform win32 -- Python 3.7.7, pytest-5.4.1, py-1.11.0, pluggy-0.13.1
rootdir: D:\SynologyDrive\CodeLearning\WIN\pytest-book\src\chapter-2, inifile: pytest.ini
plugins: allure-pytest-2.13.2
collected 1 item
test_pdb.py F
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> traceback >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
def test_fail():
x = 1
> assert x == 0
E assert 1 == 0
test_pdb.py:3: AssertionError
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> entering PDB >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> PDB post_mortem (IO-capturing turned off) >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
> d:\synologydrive\codelearning\win\pytest-book\src\chapter-2\test_pdb.py(3)test_fail()
-> assert x == 0
(Pdb) import sys
(Pdb) sys.last_value
AssertionError('assert 1 == 0')
(Pdb) sys.last_type
<class 'AssertionError'>
(Pdb) sys.last_traceback
<traceback object at 0x00000157D9A21688>
(Pdb) exit
======================================================================================================= short test summary info =======================================================================================================
FAILED test_pdb.py::test_fail - assert 1 == 0
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! _pytest.outcomes.Exit: Quitting debugger !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
========================================================================================================= 1 failed in 56.14s ==========================================================================================================
PS D:\SynologyDrive\CodeLearning\WIN\pytest-book\src\chapter-2>
开始执行时就加载PDB环境
通过以下命令，pytest允许在每个测试用例开始执行时就加载PDB环境：
设置断点
通常可以通过在代码行号附近单击具体行设置一个断点，在单击后运行会停下来。如图所示。
也可以在测试用例代码中添加import pdb;pdb.set_trace()，当其被调用时，pytest会停止这条用例的输出，其他用例不受影响。通过continue命令，退出PDB环境，并继续执行用例。
代码如下：
def test_fail():
x = 1
import pdb
pdb.set_trace()
assert x == 0 执行结果如下，在进行(Pdb)后，输入x，返回1。输入import sys，无返回。输入sys.path，返回当前系统路径。输入continue，用例接着运行，输出结果如下。
D:\SynologyDrive\CodeLearning\WIN\pytest-book\venv\Scripts\python.exe "C:/Program Files/JetBrains/PyCharm Community Edition 2022.3.2/plugins/python-ce/helpers/pycharm/_jb_pytest_runner.py" --path D:\SynologyDrive\CodeLearning\WIN\pytest-book\src\chapter-2\test_pdb.py
Testing started at 21:07 ...
Launching pytest with arguments D:\SynologyDrive\CodeLearning\WIN\pytest-book\src\chapter-2\test_pdb.py in D:\SynologyDrive\CodeLearning\WIN\pytest-book\src\chapter-2
============================= test session starts =============================
platform win32 -- Python 3.7.7, pytest-5.4.1, py-1.11.0, pluggy-0.13.1 -- D:\SynologyDrive\CodeLearning\WIN\pytest-book\venv\Scripts\python.exe
cachedir: .pytest_cache
rootdir: D:\SynologyDrive\CodeLearning\WIN\pytest-book\src\chapter-2, inifile: pytest.ini
plugins: allure-pytest-2.13.2, collect-formatter2-0.1.3
collecting ... collected 1 item
test_pdb.py::test_fail
>>>>>>>>>>>>>>>>>>> PDB set_trace (IO-capturing turned off) >>>>>>>>>>>>>>>>>>>
> d:\synologydrive\codelearning\win\pytest-book\src\chapter-2\test_pdb.py(5)test_fail()
-> assert x == 0
(Pdb) 1
(Pdb) (Pdb) ['D:\\SynologyDrive\\CodeLearning\\WIN\\pytest-book\\src\\chapter-2', 'C:\\Program Files\\JetBrains\\PyCharm Community Edition 2022.3.2\\plugins\\python-ce\\helpers\\pycharm', 'D:\\SynologyDrive\\CodeLearning\\WIN\\pytest-book', 'C:\\Users\\guoliang\\AppData\\Local\\Programs\\Python\\Python37\\python37.zip', 'C:\\Users\\guoliang\\AppData\\Local\\Programs\\Python\\Python37\\DLLs', 'C:\\Users\\guoliang\\AppData\\Local\\Programs\\Python\\Python37\\lib', 'C:\\Users\\guoliang\\AppData\\Local\\Programs\\Python\\Python37', 'D:\\SynologyDrive\\CodeLearning\\WIN\\pytest-book\\venv', 'D:\\SynologyDrive\\CodeLearning\\WIN\\pytest-book\\venv\\lib\\site-packages']
(Pdb)
>>>>>>>>>>>>>>>>>>>>> PDB continue (IO-capturing resumed) >>>>>>>>>>>>>>>>>>>>>
FAILED [100%]
test_pdb.py:0 (test_fail)
1 != 0
Expected :0
Actual :1
<Click to see difference>
def test_fail():
x = 1
import pdb
pdb.set_trace()
> assert x == 0
E assert 1 == 0
E +1
E -0
test_pdb.py:5: AssertionError
================================== FAILURES ===================================
__________________________________ test_fail __________________________________
def test_fail():
x = 1
import pdb
pdb.set_trace()
> assert x == 0
E assert 1 == 0
E +1
E -0
test_pdb.py:5: AssertionError
=========================== short test summary info ===========================
FAILED test_pdb.py::test_fail - assert 1 == 0
============================= 1 failed in 31.71s ==============================
Process finished with exit code 1
使用内置的中断函数
Python 3.7中有一个内置breakpoint()函数。pytest可以在以下场景中使用：
当breakpoint()被调用，并且PYTHONBREAKPOINT为None时，pytest会使用内部自定义的PDB代替系统的PDB，测试执行结束时，自动切换回系统自带的PDB。
当加上--pdb选项时，breakpoint()和测试发生错误时，都会调用内部自定义的PDB，--pdbcls选项允许指定一个用户自定义的PDB类。
错误句柄
这是pytest 5.0版本新增特性，在测试中发生段错误或者超时的情况下，faulthandler标准模块可以转存Python的回溯信息，它在pytest的执行中默认为已加载，使用-p no：faulthandler选项可以关闭它。同样，faulthandler_timeout=X配置项可用于当测试用例的完成时间超过X秒时，转存所有线程的Python回溯信息。
举例说明，在配置文件中设置测试执行的超时时间为5s，代码如下：
[pytest]
faulthandler_timeout=5 在测试用例中添加等待7s的操作，代码如下：
import time
def test_faulthandler():
time.sleep(7)
assert 1 当默认已加载faulthandler时，输入pytest-q test_fault_handler.py，执行结果如下，显示Timeout(0：00：05)。在执行刚超过5s的时候会打印出回溯信息，但不会中断测试的执行。
执行结果如下：
PS D:\SynologyDrive\CodeLearning\WIN\pytest-book\src\chapter-2> pytest -q .\test_fault_handler.py
Timeout (0:00:05)!
Thread 0x00005e58 (most recent call first):
File "D:\SynologyDrive\CodeLearning\WIN\pytest-book\src\chapter-2\test_fault_handler.py", line 4 in test_faulthandler
File "c:\users\guoliang\appdata\local\programs\python\python37\lib\site-packages\_pytest\python.py", line 184 in pytest_pyfunc_call
File "c:\users\guoliang\appdata\local\programs\python\python37\lib\site-packages\pluggy\callers.py", line 187 in _multicall
File "c:\users\guoliang\appdata\local\programs\python\python37\lib\site-packages\pluggy\manager.py", line 87 in <lambda>
File "c:\users\guoliang\appdata\local\programs\python\python37\lib\site-packages\pluggy\manager.py", line 93 in _hookexec
File "c:\users\guoliang\appdata\local\programs\python\python37\lib\site-packages\pluggy\hooks.py", line 286 in __call__
File "c:\users\guoliang\appdata\local\programs\python\python37\lib\site-packages\_pytest\python.py", line 1479 in runtest
File "c:\users\guoliang\appdata\local\programs\python\python37\lib\site-packages\_pytest\runner.py", line 135 in pytest_runtest_call
File "c:\users\guoliang\appdata\local\programs\python\python37\lib\site-packages\pluggy\callers.py", line 187 in _multicall
File "c:\users\guoliang\appdata\local\programs\python\python37\lib\site-packages\pluggy\manager.py", line 87 in <lambda>
File "c:\users\guoliang\appdata\local\programs\python\python37\lib\site-packages\pluggy\manager.py", line 93 in _hookexec
File "c:\users\guoliang\appdata\local\programs\python\python37\lib\site-packages\pluggy\hooks.py", line 286 in __call__
File "c:\users\guoliang\appdata\local\programs\python\python37\lib\site-packages\_pytest\runner.py", line 217 in <lambda>
File "c:\users\guoliang\appdata\local\programs\python\python37\lib\site-packages\_pytest\runner.py", line 244 in from_call
File "c:\users\guoliang\appdata\local\programs\python\python37\lib\site-packages\_pytest\runner.py", line 217 in call_runtest_hook
File "c:\users\guoliang\appdata\local\programs\python\python37\lib\site-packages\_pytest\runner.py", line 186 in call_and_report
File "c:\users\guoliang\appdata\local\programs\python\python37\lib\site-packages\_pytest\runner.py", line 100 in runtestprotocol
File "c:\users\guoliang\appdata\local\programs\python\python37\lib\site-packages\_pytest\runner.py", line 85 in pytest_runtest_protocol
File "c:\users\guoliang\appdata\local\programs\python\python37\lib\site-packages\pluggy\callers.py", line 187 in _multicall
File "c:\users\guoliang\appdata\local\programs\python\python37\lib\site-packages\pluggy\manager.py", line 87 in <lambda>
File "c:\users\guoliang\appdata\local\programs\python\python37\lib\site-packages\pluggy\manager.py", line 93 in _hookexec
File "c:\users\guoliang\appdata\local\programs\python\python37\lib\site-packages\pluggy\hooks.py", line 286 in __call__
File "c:\users\guoliang\appdata\local\programs\python\python37\lib\site-packages\_pytest\main.py", line 272 in pytest_runtestloop
File "c:\users\guoliang\appdata\local\programs\python\python37\lib\site-packages\pluggy\callers.py", line 187 in _multicall
File "c:\users\guoliang\appdata\local\programs\python\python37\lib\site-packages\pluggy\manager.py", line 87 in <lambda>
File "c:\users\guoliang\appdata\local\programs\python\python37\lib\site-packages\pluggy\manager.py", line 93 in _hookexec
File "c:\users\guoliang\appdata\local\programs\python\python37\lib\site-packages\pluggy\hooks.py", line 286 in __call__
File "c:\users\guoliang\appdata\local\programs\python\python37\lib\site-packages\_pytest\main.py", line 247 in _main
File "c:\users\guoliang\appdata\local\programs\python\python37\lib\site-packages\_pytest\main.py", line 191 in wrap_session
File "c:\users\guoliang\appdata\local\programs\python\python37\lib\site-packages\_pytest\main.py", line 240 in pytest_cmdline_main
File "c:\users\guoliang\appdata\local\programs\python\python37\lib\site-packages\pluggy\callers.py", line 187 in _multicall
File "c:\users\guoliang\appdata\local\programs\python\python37\lib\site-packages\pluggy\manager.py", line 87 in <lambda>
File "c:\users\guoliang\appdata\local\programs\python\python37\lib\site-packages\pluggy\manager.py", line 93 in _hookexec
File "c:\users\guoliang\appdata\local\programs\python\python37\lib\site-packages\pluggy\hooks.py", line 286 in __call__
File "c:\users\guoliang\appdata\local\programs\python\python37\lib\site-packages\_pytest\config\__init__.py", line 125 in main
File "C:\Users\guoliang\AppData\Local\Programs\Python\Python37\Scripts\pytest.exe\__main__.py", line 9 in <module>
File "c:\users\guoliang\appdata\local\programs\python\python37\lib\runpy.py", line 85 in _run_code
File "c:\users\guoliang\appdata\local\programs\python\python37\lib\runpy.py", line 193 in _run_module_as_main
. [100%]
1 passed in 7.09s
PS D:\SynologyDrive\CodeLearning\WIN\pytest-book\src\chapter-2>
接下来看一下去掉faulthandler的情况，超时并不会触发回溯信息的打印，输入pytest -q -p no：faulthandler test_fault_handler.py之后的结果如下：
PS D:\SynologyDrive\CodeLearning\WIN\pytest-book\src\chapter-2> pytest -q -p no:faulthandler test_fault_handler.py
. [100%]
1 passed in 7.02s
PS D:\SynologyDrive\CodeLearning\WIN\pytest-book\src\chapter-2>
注意：这个功能是从pytest -faulthandler插件合并而来的，但是有两点不同：去掉此功能时，使用-p no：faulthandler代替原来的--no-faulthandler;使用faulthandler_timeout配置项代替--faulthandler-timeout命令行选项来配置超时时间。当然，也可以使用-o faulthandler_timeout=X在命令行进行配置。