上一节我们介绍了pytest的安装和简单使用，这一节我们再加些料

pytest不仅容易编写小的测试例，也支持程序和库相关的复杂函数测试

通过python -m pytest来调用pytest

python -m pytest [...]

这和直接使用pytest命令功能相同，唯一的区别是会将当前目录加入到sys.path中.

可能的退出码

调用pytest可能产生６种不同的退出码

pytest的退出码ＡＰＩ

from pytest import ExitCode

如果你需要在某些场景下定制ExiCode,可以使用pytest-custom_exit_code插件

pytest帮助命令

pytest --version   # shows where pytest was imported from
pytest --fixtures  # show available builtin function arguments
pytest -h | --help # show help on command line and config file options

在测试例失败指定个数后停止pytest

pytest -x           # stop after first failure
pytest --maxfail=2  # stop after two failures

选择指定的测试例运行

pytest支持多种方式选择要运行的测试例

运行指定的模块

pytest test_mod.py

运行指定的目录

pytest testing/

指定关键字运行

pytest -k "MyClass and not method"

上面的命令将会运行名字满足上面字符串表达式的用例，字符串表达式可以包含文件名，类名，函数名。上面的例子会运行TestMyClass.test_something，但不会运行TestMyClass.test_method_simple.

指定node ids运行

每个测试例都有一个唯一的nodeid,由模块名::类名::函数名组成。

运行指定模块中的测试例:

pytest test_mod.py::test_func

运行指定模块中指定类中的指定函数

pytest test_mod.py::test_func

指定marker表达式运行

pytest -m slow

上面的命令将会运行所有被@pytest.mark.slow 装饰的测试例　

运行指定包中的测试例

pytest --pyargs pkg.testing

修改python打印traceback的方式

pytest --showlocals # show local variables in tracebacks
pytest -l           # show local variables (shortcut)pytest --tb=auto    # (default) 'long' tracebacks for the first and last# entry, but 'short' style for the other entries
pytest --tb=long    # exhaustive, informative traceback formatting
pytest --tb=short   # shorter traceback format
pytest --tb=line    # only one line per failure
pytest --tb=native  # Python standard library formatting
pytest --tb=no      # no traceback at all

"--full-trace”会在发生错误时打印很长的回溯栈，同时也能保证在KeyboardInterrupt (Ctrl+C)时打印栈.

在测试长时间运行不中止时我们用Ctrl+C中止后十分有用，便于我们发现问题所在。

通常情况下，pytests会捕获Ctrl+C因此不会打印栈信息。使用这个选项能够确保显示trace信息。

详细的总结报告

"-r"选项用于在测试结束时显示一个简短的测试总结信息。这便于我们在大的测试套件中获取失败，跳过用例的清晰信息。

默认情况下,pytest使用"fE"来显示失败和错误.

举例：

# content of test_example.py
import pytest@pytest.fixture
def error_fixture():assert 0def test_ok():print("ok")def test_fail():assert 0def test_error(error_fixture):passdef test_skip():pytest.skip("skipping this test")def test_xfail():pytest.xfail("xfailing this test")@pytest.mark.xfail(reason="always xfail")
def test_xpass():pass

$ pytest -ra
=========================== test session starts ============================
platform linux -- Python 3.x.y, pytest-5.x.y, py-1.x.y, pluggy-0.x.y
cachedir: $PYTHON_PREFIX/.pytest_cache
rootdir: $REGENDOC_TMPDIR
collected 6 itemstest_example.py .FEsxX                                               [100%]================================== ERRORS ==================================
_______________________ ERROR at setup of test_error _______________________@pytest.fixturedef error_fixture():
>       assert 0
E       assert 0test_example.py:6: AssertionError
================================= FAILURES =================================
________________________________ test_fail _________________________________def test_fail():
>       assert 0
E       assert 0test_example.py:14: AssertionError
========================= short test summary info ==========================
SKIPPED [1] $REGENDOC_TMPDIR/test_example.py:22: skipping this test
XFAIL test_example.py::test_xfailreason: xfailing this test
XPASS test_example.py::test_xpass always xfail
ERROR test_example.py::test_error - assert 0
FAILED test_example.py::test_fail - assert 0
== 1 failed, 1 passed, 1 skipped, 1 xfailed, 1 xpassed, 1 error in 0.12s ===

-r选项后面可以接受一系列字符，'a'表示除了所有通过以外的测试例

下面是所有可以使用的字符:

• f - failed
• E - error
• s - skipped
• x - xfailed
• X - xpassed
• p - passed
• P - passed with output

用于选择和反选择的特殊字符:

• a - all except pP
• A - all
• N - none, this can be used to display nothing (since fE is the default)

可以指定多个字符，下面的例子中只显示失败和跳过的测试例:

=========================== test session starts ============================
platform linux -- Python 3.x.y, pytest-5.x.y, py-1.x.y, pluggy-0.x.y
cachedir: $PYTHON_PREFIX/.pytest_cache
rootdir: $REGENDOC_TMPDIR
collected 6 itemstest_example.py .FEsxX                                               [100%]================================== ERRORS ==================================
_______________________ ERROR at setup of test_error _______________________@pytest.fixturedef error_fixture():
>       assert 0
E       assert 0test_example.py:6: AssertionError
================================= FAILURES =================================
________________________________ test_fail _________________________________def test_fail():
>       assert 0
E       assert 0test_example.py:14: AssertionError
========================= short test summary info ==========================
FAILED test_example.py::test_fail - assert 0
SKIPPED [1] $REGENDOC_TMPDIR/test_example.py:22: skipping this test
== 1 failed, 1 passed, 1 skipped, 1 xfailed, 1 xpassed, 1 error in 0.12s ===

使用p展示通过的测试例，P添加额外的"PASSES"来展示:

$ pytest -rpP
=========================== test session starts ============================
platform linux -- Python 3.x.y, pytest-5.x.y, py-1.x.y, pluggy-0.x.y
cachedir: $PYTHON_PREFIX/.pytest_cache
rootdir: $REGENDOC_TMPDIR
collected 6 itemstest_example.py .FEsxX                                               [100%]================================== ERRORS ==================================
_______________________ ERROR at setup of test_error _______________________@pytest.fixturedef error_fixture():
>       assert 0
E       assert 0test_example.py:6: AssertionError
================================= FAILURES =================================
________________________________ test_fail _________________________________def test_fail():
>       assert 0
E       assert 0test_example.py:14: AssertionError
================================== PASSES ==================================
_________________________________ test_ok __________________________________
--------------------------- Captured stdout call ---------------------------
ok
========================= short test summary info ==========================
PASSED test_example.py::test_ok
== 1 failed, 1 passed, 1 skipped, 1 xfailed, 1 xpassed, 1 error in 0.12s ===

失败时使用PDB(Python Debugger)

pytest --pdb

控制使用PDB的条件

pytest -x --pdb   # drop to PDB on first failure, then end test session
pytest --pdb --maxfail=3  # drop to PDB for first three failures

注意当失败时，异常信息会存储到sys.last_value, sys.last_type 和sys.last_traceback. 在交互模式下，这允许我们在用debug工具在事后进行分析。你也可以手动访问异常信息:

>>> import sys
>>> sys.last_traceback.tb_lineno
42
>>> sys.last_value
AssertionError('assert result == "ok"',)

在测试开始时进入PDB

pytest --trace

上面的命令将会在每个测试例开始时进入PDB.

使用断点

要在代码里设置断点，使用原生的Python方法:

    def test_two(self):x = "hello"import pdbpdb.set_trace()assert hasattr(x, "check")

使用内置的breakpoint函数

python3.7提供了内置的breakpoint函数，pytest支持的breakpoint函数有以下行为:

• When breakpoint() is called and PYTHONBREAKPOINT is set to the default value, pytest will use the custom internal PDB trace UI instead of the system default Pdb.
• When tests are complete, the system will default back to the system Pdb trace UI.
• With --pdb passed to pytest, the custom internal Pdb trace UI is used with both breakpoint() and failed tests/unhandled exceptions.
• --pdbcls can be used to specify a custom debugger class.

分析测试执行时间

得到执行最慢的１０个测试

pytest --durations=10

默认情况下，pytest不显示执行时间特别短的测试(<0.01s)，除非使用-vv选项。

===================================================================================================== slowest 2 test durations ======================================================================================================
1.81s call     test_class.py::TestClass::test_two
0.01s setup    test_tmpdir.py::test_needsfiles

缺陷处理

从5.0版本开始支持

faulthandler标准库用于在产生段错误或超时时dump Python tracebacks. 

这个模块在pytest中自动加载，除非使用 -p no:faulthandler.

 faulthandler_timeout=X配置可以用于 dump所有线程的traceback，如果一个测试例运行超过X秒（在Windows上不支持）.

提前加载插件

pytest -p mypluginmodule

禁用插件

pytest -p no:doctest

在Python代码中使用pytest

pytest.main()

使用参数

pytest.main(["-x", "mytestdir"])

指定额外插件

# content of myinvoke.py
import pytestclass MyPlugin:def pytest_sessionfinish(self):print("*** test run reporting finishing")pytest.main(["-qq"], plugins=[MyPlugin()])

$ python myinvoke.py
.FEsxX.                                                              [100%]*** test run reporting finishing================================== ERRORS ==================================
_______________________ ERROR at setup of test_error _______________________@pytest.fixturedef error_fixture():
>       assert 0
E       assert 0test_example.py:6: AssertionError
================================= FAILURES =================================
________________________________ test_fail _________________________________def test_fail():
>       assert 0
E       assert 0test_example.py:14: AssertionError
========================= short test summary info ==========================
FAILED test_example.py::test_fail - assert 0
ERROR test_example.py::test_error - assert 0