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12、pytest -- 缓存:记录执行的状态

2019年12月02日 16:28  | 萬仟网IT编程  | 我要评论

目录

往期索引:

pytest会将本轮测试的执行状态写入到.pytest_cache文件夹,这个行为是由自带的cacheprovider插件来实现的;

注意:

pytest默认将测试执行的状态写入到根目录中的.pytest_cache文件夹,我们也可以通过在pytest.ini中配置cache_dir选项来自定义缓存的目录,它可以是相对路径,也可以是绝对路径;

相对路径指的是相对于pytest.ini文件所在的目录;例如,我们把这一章的缓存和源码放在一起:

src/chapter-12/pytest.ini中添加如下配置:

[pytest]
cache_dir = .pytest-cache

这样,即使我们在项目的根目录下执行src/chapter-12/中的用例,也只会在pytest-chinese-doc/src/chapter-12/.pytest_cache中生成缓存,而不再是pytest-chinese-doc/.pytest_cache中;

pytest-chinese-doc (5.1.3) 
λ pipenv run pytest src/chapter-12

1. cacheprovider插件

在介绍这个插件之前,我们先看一个简单例子:

# src/chapter-12/test_failed.py

import pytest


@pytest.mark.parametrize('num', [1, 2])
def test_failed(num):
    assert num == 1


# src\chapter-12\test_pass.py

def test_pass():
    assert 1

我们有两个简单的测试模块,首先我们来执行一下它们:

λ pipenv run pytest -q src/chapter-12/
.f.                                                                [100%] 
=============================== failures ================================ 
____________________________ test_failed[2] _____________________________

num = 2

    @pytest.mark.parametrize('num', [1, 2])
    def test_failed(num):
>       assert num == 1
e       assert 2 == 1

src\chapter-12\test_failed.py:27: assertionerror
1 failed, 2 passed in 0.08s

可以看到一共收集到三个测试用例,其中有一个失败,另外两个成功的,并且两个执行成功的用例分属不同的测试模块;

同时,pytest也在src/chapter-12/的目录下生成缓存文件夹(.pytest_cache),具体的目录结构如下所示:

src
├───chapter-12
│   │   pytest.ini  # 配置了 cache_dir = .pytest-cache
│   │   test_failed.py
│   │   test_pass.py
│   │
│   └───.pytest-cache
│       │   .gitignore
│       │   cachedir.tag
│       │   readme.md
│       │
│       └───v
│           └───cache
│                   lastfailed
│                   nodeids
│                   stepwise

现在,我们就结合上面的组织结构,具体介绍一下cacheprovider插件的功能;

1.1. --lf, --last-failed:只执行上一轮失败的用例

缓存中的lastfailed文件记录了上次失败的用例id,我们可以通过一下--cache-show命令查看它的内容:

--cache-show命令也是cacheprovider提供的新功能,它不会导致任何用例的执行;

λ pipenv run pytest src/chapter-12/ -q --cache-show 'lastfailed'
cachedir: d:\personal files\projects\pytest-chinese-doc\src\chapter-12\.pytest-cache
--------------------- cache values for 'lastfailed' --------------------- 
cache\lastfailed contains:
  {'test_failed.py::test_failed[2]': true}

no tests ran in 0.01s

我们可以看到,它记录了一个用例,为上次失败的测试用例的idtest_failed.py::test_failed[2]

下次执行时,当我们使用--lf选项,pytest在收集阶段只会选择这个失败的用例,而忽略其它的:

λ pipenv run pytest --lf --collect-only src/chapter-12/
========================== test session starts ==========================
platform win32 -- python 3.7.3, pytest-5.1.3, py-1.8.0, pluggy-0.13.0
cachedir: .pytest-cache
rootdir: d:\personal files\projects\pytest-chinese-doc\src\chapter-12, inifile: pytest.ini
collected 2 items / 1 deselected / 1 selected
<module test_failed.py>
  <function test_failed[2]>
run-last-failure: rerun previous 1 failure (skipped 2 files)

========================= 1 deselected in 0.02s =========================

我们仔细观察一下上面的回显,有一句话可能会让我们有点困惑:collected 2 items / 1 deselected / 1 selected,可我们明明有三个用例,怎么会只收集到两个呢?

实际上,--lf复写了用例收集阶段的两个钩子方法:pytest_ignore_collect(path, config)pytest_collection_modifyitems(session, config, items)

我们来先看看pytest_ignore_collect(path, config),如果它的结果返回true,就忽略path路径中的用例;

# _pytest/cacheprovider.py

    def last_failed_paths(self):
        """returns a set with all paths()s of the previously failed nodeids (cached).
        """
        try:
            return self._last_failed_paths
        except attributeerror:
            rootpath = path(self.config.rootdir)
            result = {rootpath / nodeid.split("::")[0] for nodeid in self.lastfailed}
            result = {x for x in result if x.exists()}
            self._last_failed_paths = result
            return result

    def pytest_ignore_collect(self, path):
        """
        ignore this file path if we are in --lf mode and it is not in the list of
        previously failed files.
        """
        if self.active and self.config.getoption("lf") and path.isfile():
            last_failed_paths = self.last_failed_paths()
            if last_failed_paths:
                skip_it = path(path) not in self.last_failed_paths()
                if skip_it:
                    self._skipped_files += 1
                return skip_it

可以看到,如果当前收集的文件,不在上一次失败的路径集合内,就会忽略这个文件,所以这次执行就不会到test_pass.py中收集用例了,故而只收集到两个用例;并且pytest.ini也在忽略的名单上,所以实际上是跳过两个文件:(skipped 2 files)

至于pytest_collection_modifyitems(session, config, items)钩子方法,我们在下一节和--ff命令一起看;

1.2. --ff, --failed-first:先执行上一轮失败的用例,再执行其它的

我们先通过实践看看这个命令的效果,再去分析它的实现:

λ pipenv run pytest --collect-only -s --ff src/chapter-12/
========================== test session starts ========================== 
platform win32 -- python 3.7.3, pytest-5.1.3, py-1.8.0, pluggy-0.13.0
cachedir: .pytest-cache
rootdir: d:\personal files\projects\pytest-chinese-doc\src\chapter-12, inifile: pytest.ini
collected 3 items
<module test_failed.py>
  <function test_failed[2]>
  <function test_failed[1]>
<module test_pass.py>
  <function test_pass>
run-last-failure: rerun previous 1 failure first

========================= no tests ran in 0.02s =========================

我们可以看到一共收集到三个测试用例,和正常的收集顺序相比,上一轮失败的test_failed.py::test_failed[2]用例在最前面,将优先执行;

实际上,-ff只复写了钩子方法:pytest_collection_modifyitems(session, config, items),它可以过滤或者重新排序收集到的用例:

# _pytest/cacheprovider.py

    def pytest_collection_modifyitems(self, session, config, items):
        ...

                if self.config.getoption("lf"):
                    items[:] = previously_failed
                    config.hook.pytest_deselected(items=previously_passed)
                else:  # --failedfirst
                    items[:] = previously_failed + previously_passed

        ...

可以看到,如果使用的是lf,就把之前成功的用例状态置为deselected,这轮执行就会忽略它们;如果使用的是-ff,只是将之前失败的用例,顺序调到前面;

另外,我们也可以看到lf的优先级要高于ff,所以它们同时使用的话,ff是不起作用的;

1.3. --nf, --new-first:先执行新加的或修改的用例,再执行其它的

缓存中的nodeids文件记录了上一轮执行的所有的用例:

λ pipenv run pytest src/chapter-12 --cache-show 'nodeids'
========================== test session starts ==========================
platform win32 -- python 3.7.3, pytest-5.1.3, py-1.8.0, pluggy-0.13.0
cachedir: .pytest-cache
rootdir: d:\personal files\projects\pytest-chinese-doc\src\chapter-12, inifile: pytest.ini
cachedir: d:\personal files\projects\pytest-chinese-doc\src\chapter-12\.pytest-cache
---------------------- cache values for 'nodeids' -----------------------
cache\nodeids contains:
  ['test_failed.py::test_failed[1]',
   'test_failed.py::test_failed[2]',
   'test_pass.py::test_pass']

========================= no tests ran in 0.01s =========================

我们看到上一轮共执行了三个测试用例;

现在我们在test_pass.py中新加一个用例,并修改一下test_failed.py文件中的用例(但是不添加新用例):

# src\chapter-12\test_pass.py

def test_pass():
    assert 1


def test_new_pass():
    assert 1

现在我们再来执行一下收集命令:

λ pipenv run pytest --collect-only -s --nf src/chapter-12/
========================== test session starts ==========================
platform win32 -- python 3.7.3, pytest-5.1.3, py-1.8.0, pluggy-0.13.0
cachedir: .pytest-cache
rootdir: d:\personal files\projects\pytest-chinese-doc\src\chapter-12, inifile: pytest.ini
collected 4 items
<module test_pass.py>
  <function test_new_pass>
<module test_failed.py>
  <function test_failed[1]>
  <function test_failed[2]>
<module test_pass.py>
  <function test_pass>

========================= no tests ran in 0.03s =========================

可以看到,新加的用例顺序在最前面,其次修改过的测试用例紧接其后,最后才是旧的用例;这个行为在源码中有所体现:

# _pytest/cacheprovider.py

    def pytest_collection_modifyitems(self, session, config, items):
        if self.active:
            new_items = ordereddict()
            other_items = ordereddict()
            for item in items:
                if item.nodeid not in self.cached_nodeids:
                    new_items[item.nodeid] = item
                else:
                    other_items[item.nodeid] = item

            items[:] = self._get_increasing_order(
                new_items.values()
            ) + self._get_increasing_order(other_items.values())
        self.cached_nodeids = [x.nodeid for x in items if isinstance(x, pytest.item)]

    def _get_increasing_order(self, items):
        return sorted(items, key=lambda item: item.fspath.mtime(), reverse=true)

item.fspath.mtime()代表用例所在文件的最后修改时间,reverse=true表明是倒序排列;

items[:] = self._get_increasing_order(new_items.values()) + self._get_increasing_order(other_items.values())保证新加的用例永远在最前面;

1.4. --cache-clear:先清除所有缓存,再执行用例

直接看源码:

# _pytest/cacheprovider.py

class cache:

    ... 

    @classmethod
    def for_config(cls, config):
        cachedir = cls.cache_dir_from_config(config)
        if config.getoption("cacheclear") and cachedir.exists():
            rm_rf(cachedir)
            cachedir.mkdir()
        return cls(cachedir, config)

可以看到,它会先把已有的缓存文件夹删除(rm_rf(cachedir)),再创建一个空的同名文件夹(cachedir.mkdir()),这样会导致上述的功能失效,所以一般不使用这个命令;

1.5. 如果上一轮没有失败的用例

现在,我们清除缓存,再执行test_pass.py模块(它的用例都是能测试成功的):

λ pipenv run pytest --cache-clear -q -s src/chapter-12/test_pass.py
.
1 passed in 0.01s

这时候我们再去看一下缓存目录:

.pytest-cache
└───v
    └───cache
            nodeids
            stepwise

是不是少了什么?对!因为没有失败的用例,所以不会生成lastfailed文件,那么这个时候在使用--lf--ff会发生什么呢?我们来试试:

注意:

如果我们观察的足够仔细,就会发现现在的缓存目录和之前相比不止少了lastfailed文件,还少了cachedir.tag.gitignorereadme.md三个文件;

这是一个bug,我已经在pytest 5.3.1版本上提交了issue,预计会在之后的版本修复,如果你有兴趣深入了解一下它的成因和修复方案,可以参考这个:

luyao@nj-luyao-t460 /d/personal files/projects/pytest-chinese-doc (5.1.3) 
λ pipenv run pytest -q -s --lf src/chapter-12/test_pass.py
.
1 passed in 0.01s

luyao@nj-luyao-t460 /d/personal files/projects/pytest-chinese-doc (5.1.3) 
λ pipenv run pytest -q -s --ff src/chapter-12/test_pass.py
.
1 passed in 0.02s

可以看到,它们没有实施任何影响;为什么会这样?我们去源码里找一下答案吧;

# _pytest/cacheprovider.py

class lfplugin:
    """ plugin which implements the --lf (run last-failing) option """

    def __init__(self, config):
        ...
        self.lastfailed = config.cache.get("cache/lastfailed", {})
        ...

    def pytest_collection_modifyitems(self, session, config, items):
        ...

        if self.lastfailed:

            ...

        else:
            self._report_status = "no previously failed tests, "
            if self.config.getoption("last_failed_no_failures") == "none":
                self._report_status += "deselecting all items."
                config.hook.pytest_deselected(items=items)
                items[:] = []
            else:
                self._report_status += "not deselecting items."

可以看到,当self.lastfailed判断失败时,如果我们指定了last_failed_no_failures选项为nonepytest会忽略所有的用例(items[:] = []),否则不做任何修改(和没加--lf--ff一样),而判断self.lastfailed的依据是就是lastfailed文件;

继续看看,我们会学习到一个新的命令行选项:

# _pytest/cacheprovider.py

    group.addoption(
            "--lfnf",
            "--last-failed-no-failures",
            action="store",
            dest="last_failed_no_failures",
            choices=("all", "none"),
            default="all",
            help="which tests to run with no previously (known) failures.",
        )

来试试吧:

λ pipenv run pytest -q -s --ff --lfnf none src/chapter-12/test_pass.py

1 deselected in 0.01s

λ pipenv run pytest -q -s --ff --lfnf all src/chapter-12/test_pass.py
.
1 passed in 0.01s

注意:

--lfnf的实参只支持choices=("all", "none")

2. config.cache对象

我们可以通过pytestconfig对象去访问和设置缓存中的数据;下面是一个简单的例子:

# content of test_caching.py

import pytest
import time


def expensive_computation():
    print("running expensive computation...")


@pytest.fixture
def mydata(request):
    val = request.config.cache.get("example/value", none)
    if val is none:
        expensive_computation()
        val = 42
        request.config.cache.set("example/value", val)
    return val


def test_function(mydata):
    assert mydata == 23

我们先执行一次这个测试用例:

λ pipenv run pytest -q src/chapter-12/test_caching.py 
f                                                                   [100%]
================================ failures =================================
______________________________ test_function ______________________________

mydata = 42

    def test_function(mydata):
>       assert mydata == 23
e       assert 42 == 23

src/chapter-12/test_caching.py:43: assertionerror
-------------------------- captured stdout setup --------------------------
running expensive computation...
1 failed in 0.05s

这个时候,缓存中没有example/value,将val的值写入缓存,终端打印running expensive computation...

查看缓存,其中新加了一个文件:.pytest-cache/v/example/value

.pytest-cache/
├── .gitignore
├── cachedir.tag
├── readme.md
└── v
    ├── cache
    │   ├── lastfailed
    │   ├── nodeids
    │   └── stepwise
    └── example
        └── value

3 directories, 7 files

通过--cache-show选项查看,发现其内容正是42

λ pipenv run pytest src/chapter-12/ -q --cache-show 'example/value'
cachedir: /users/yaomeng/private/projects/pytest-chinese-doc/src/chapter-12/.pytest-cache
-------------------- cache values for 'example/value' ---------------------
example/value contains:
  42

no tests ran in 0.00s

再次执行这个用例,这个时候缓存中已经有我们需要的数据了,终端就不会再打印running expensive computation...

λ pipenv run pytest -q src/chapter-12/test_caching.py 
f                                                                   [100%]
================================ failures =================================
______________________________ test_function ______________________________

mydata = 42

    def test_function(mydata):
>       assert mydata == 23
e       assert 42 == 23

src/chapter-12/test_caching.py:43: assertionerror
1 failed in 0.04s

3. stepwise

试想一下,现在有这么一个场景:我们想要在遇到第一个失败的用例时退出执行,并且下次还是从这个用例开始执行;

以下面这个测试模块为例:

# src/chapter-12/test_sample.py

def test_one():
    assert 1


def test_two():
    assert 0


def test_three():
    assert 1


def test_four():
    assert 0


def test_five():
    assert 1

我们先执行一下测试:pipenv run pytest --cache-clear --sw src/chapter-12/test_sample.py

λ pipenv run pytest --cache-clear --sw -q src/chapter-12/test_sample.py
.f
================================= failures =================================
_________________________________ test_two _________________________________

    def test_two():
>       assert 0
e       assert 0

src/chapter-12/test_sample.py:28: assertionerror
!!!!!! interrupted: test failed, continuing from this test next run. !!!!!!!
1 failed, 1 passed in 0.13s

使用--cache-clear清除之前的缓存,使用--sw, --stepwise使其在第一个失败的用例处退出执行;

现在我们的缓存文件中lastfailed记录了这次执行失败的用例,即为test_two()nodeids记录了所有的测试用例;特殊的是,stepwise记录了最近一次失败的测试用例,这里也是test_two()

接下来,我们用--sw的方式再次执行:pytest首先会读取stepwise中的值,并将其作为第一个用例开始执行;

λ pipenv run pytest --sw -q src/chapter-12/test_sample.py
f
================================= failures =================================
_________________________________ test_two _________________________________

    def test_two():
>       assert 0
e       assert 0

src/chapter-12/test_sample.py:28: assertionerror
!!!!!! interrupted: test failed, continuing from this test next run. !!!!!!!
1 failed, 1 deselected in 0.12s

可以看到,test_two()作为第一个用例开始执行,在第一个失败处退出;

其实,pytest还提供了一个--stepwise-skip的命令行选项,它会忽略第一个失败的用例,在第二个失败处退出执行;我们来试一下:

λ pipenv run pytest --sw --stepwise-skip -q src/chapter-12/test_sample.py
f.f
=============================== failures ================================ 
_______________________________ test_two ________________________________

    def test_two():
>       assert 0
e       assert 0

src\chapter-12\test_sample.py:28: assertionerror
_______________________________ test_four _______________________________

    def test_four():
>       assert 0
e       assert 0

src\chapter-12\test_sample.py:36: assertionerror
!!!!! interrupted: test failed, continuing from this test next run. !!!!! 2 failed, 1 passed, 1 deselected in 0.16s

这个时候,在第二个失败的用例test_four()处退出执行,同时stepwise文件的值也改成了"test_sample.py::test_four"

其实,本章所有的内容都可以在源码的_pytest/cacheprovider.py文件中体现,如果能结合源码学习,会有事半功倍的效果;

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