Pytest Pytest源码分析

Pytest源码分析

By:授客 QQ:1033553122

测试环境

pytest 5.4.3

测试脚本mytest.py

#!/usr/bin/env python
# -*- coding:utf-8 -*-

import pytest

def test_func(): # test开头的测试函数
    print("test_func")
    assert 1 # 断言成功

if __name__ == '__main__':
    pytest.main() # 执行测试

源码分析

测试脚本mytest.py

import pytest

运行pytest/__init__.py，主要做了两件事情

1. 从_pytest导入后续需要用的依赖包
2. 通过_pytest/compat.py模块的_setup_collect_fakemodule()建立一个伪模块pytest.collect

pytest/__init__.py

# PYTHON_ARGCOMPLETE_OK
"""
pytest: unit and functional testing with Python.
"""
from _pytest import __version__
from _pytest.assertion import register_assert_rewrite
from _pytest.compat import _setup_collect_fakemodule
from _pytest.config import cmdline
from _pytest.config import ExitCode
from _pytest.config import hookimpl
from _pytest.config import hookspec
from _pytest.config import main
from _pytest.config import UsageError
from _pytest.debugging import pytestPDB as __pytestPDB
from _pytest.fixtures import fillfixtures as _fillfuncargs
from _pytest.fixtures import fixture
from _pytest.fixtures import yield_fixture
from _pytest.freeze_support import freeze_includes
from _pytest.main import Session
from _pytest.mark import MARK_GEN as mark
from _pytest.mark import param
from _pytest.nodes import Collector
from _pytest.nodes import File
from _pytest.nodes import Item
from _pytest.outcomes import exit
from _pytest.outcomes import fail
from _pytest.outcomes import importorskip
from _pytest.outcomes import skip
from _pytest.outcomes import xfail
from _pytest.python import Class
from _pytest.python import Function
from _pytest.python import Instance
from _pytest.python import Module
from _pytest.python import Package
from _pytest.python_api import approx
from _pytest.python_api import raises
from _pytest.recwarn import deprecated_call
from _pytest.recwarn import warns
from _pytest.warning_types import PytestAssertRewriteWarning
from _pytest.warning_types import PytestCacheWarning
from _pytest.warning_types import PytestCollectionWarning
from _pytest.warning_types import PytestConfigWarning
from _pytest.warning_types import PytestDeprecationWarning
from _pytest.warning_types import PytestExperimentalApiWarning
from _pytest.warning_types import PytestUnhandledCoroutineWarning
from _pytest.warning_types import PytestUnknownMarkWarning
from _pytest.warning_types import PytestWarning


set_trace = __pytestPDB.set_trace

__all__ = [
    "__version__",
    "_fillfuncargs",
    "approx",
    "Class",
    "cmdline",
    "Collector",
    "deprecated_call",
    "exit",
    "ExitCode",
    "fail",
    "File",
    "fixture",
    "freeze_includes",
    "Function",
    "hookimpl",
    "hookspec",
    "importorskip",
    "Instance",
    "Item",
    "main",
    "mark",
    "Module",
    "Package",
    "param",
    "PytestAssertRewriteWarning",
    "PytestCacheWarning",
    "PytestCollectionWarning",
    "PytestConfigWarning",
    "PytestDeprecationWarning",
    "PytestExperimentalApiWarning",
    "PytestUnhandledCoroutineWarning",
    "PytestUnknownMarkWarning",
    "PytestWarning",
    "raises",
    "register_assert_rewrite",
    "Session",
    "set_trace",
    "skip",
    "UsageError",
    "warns",
    "xfail",
    "yield_fixture",
]

_setup_collect_fakemodule() # 建立一个伪模块`pytest.collect`
del _setup_collect_fakemodule

_pytest/compat.py

_setup_collect_fakemodule函数

COLLECT_FAKEMODULE_ATTRIBUTES = (
    "Collector",
    "Module",
    "Function",
    "Instance",
    "Session",
    "Item",
    "Class",
    "File",
    "_fillfuncargs",
)


def _setup_collect_fakemodule() -> None:
    from types import ModuleType
    import pytest

    # Types ignored because the module is created dynamically.
    pytest.collect = ModuleType("pytest.collect")  # type: ignore
    pytest.collect.__all__ = []  # type: ignore  # used for setns
    for attr_name in COLLECT_FAKEMODULE_ATTRIBUTES:
        setattr(pytest.collect, attr_name, getattr(pytest, attr_name))  # type: ignore

测试脚本myptest.py

pytest.main()

这里的main函数为从_pytest/config/__init__.py定义的全局函数--main函数

_pytest/config/__init__.py

_pytest/config/__init__.py main函数定义

主要用于获取Config对象config，然后通过config.hook.pytest_cmdline_main执行测试

def main(args=None, plugins=None) -> Union[int, ExitCode]:
    """ return exit code, after performing an in-process test run.

    :arg args: list of command line arguments.

    :arg plugins: list of plugin objects to be auto-registered during
                  initialization.
    """
    try:
        try:
            config = _prepareconfig(args, plugins) 
        except ConftestImportFailure as e:
            exc_info = ExceptionInfo(e.excinfo)
            tw = TerminalWriter(sys.stderr)
            tw.line(
                "ImportError while loading conftest '{e.path}'.".format(e=e), red=True
            )
            exc_info.traceback = exc_info.traceback.filter(filter_traceback)
            exc_repr = (
                exc_info.getrepr(style="short", chain=False)
                if exc_info.traceback
                else exc_info.exconly()
            )
            formatted_tb = str(exc_repr)
            for line in formatted_tb.splitlines():
                tw.line(line.rstrip(), red=True)
            return ExitCode.USAGE_ERROR
        else:
            try:
                ret = config.hook.pytest_cmdline_main(
                    config=config
                )  # type: Union[ExitCode, int]
                try:
                    return ExitCode(ret)
                except ValueError:
                    return ret
            finally:
                config._ensure_unconfigure()
    except UsageError as e:
        tw = TerminalWriter(sys.stderr)
        for msg in e.args:
            tw.line("ERROR: {}
".format(msg), red=True)
        return ExitCode.USAGE_ERROR

_pytest/config/__init__.py _prepareconfig函数定义

主要是获取并返回Config对象config，该对象通过函数pluginmanager.hook.pytest_cmdline_parse返回

def _prepareconfig(
    args: Optional[Union[py.path.local, List[str]]] = None, plugins=None
):
    if args is None:
        args = sys.argv[1:]
    elif isinstance(args, py.path.local):
        args = [str(args)]
    elif not isinstance(args, list):
        msg = "`args` parameter expected to be a list of strings, got: {!r} (type: {})"
        raise TypeError(msg.format(args, type(args)))

    config = get_config(args, plugins)
    pluginmanager = config.pluginmanager
    try:
        if plugins:
            for plugin in plugins:
                if isinstance(plugin, str):
                    pluginmanager.consider_pluginarg(plugin)
                else:
                    pluginmanager.register(plugin)
        return pluginmanager.hook.pytest_cmdline_parse(
            pluginmanager=pluginmanager, args=args
        )
    except BaseException:
        config._ensure_unconfigure()
        raise

_pytest/config/__init__.py get_config函数定义

主要是构造Config对象

# Plugins that cannot be disabled via "-p no:X" currently.
essential_plugins = (
    "mark",
    "main",
    "runner",
    "fixtures",
    "helpconfig",  # Provides -p.
)

default_plugins = essential_plugins + (
    "python",
    "terminal",
    "debugging",
    "unittest",
    "capture",
    "skipping",
    "tmpdir",
    "monkeypatch",
    "recwarn",
    "pastebin",
    "nose",
    "assertion",
    "junitxml",
    "resultlog",
    "doctest",
    "cacheprovider",
    "freeze_support",
    "setuponly",
    "setupplan",
    "stepwise",
    "warnings",
    "logging",
    "reports",
    "faulthandler",
)

builtin_plugins = set(default_plugins)
builtin_plugins.add("pytester")


def get_config(args=None, plugins=None):
    # subsequent calls to main will create a fresh instance
    pluginmanager = PytestPluginManager()  # PytestPluginManager 继承于 PluginManager
    config = Config(
        pluginmanager,
        invocation_params=Config.InvocationParams(
            args=args or (), plugins=plugins, dir=Path().resolve()
        ),
    )

    if args is not None:
        # Handle any "-p no:plugin" args.
        pluginmanager.consider_preparse(args, exclude_only=True)
    for spec in default_plugins:
        pluginmanager.import_plugin(spec) # 为对象导入插件
    return config

_pytest/config/__init__.py Config构造函数定义

构造函数参数pluginmanager接收了外部传入的PytestPluginManager实例对象，该参数被赋值给 self.pluginmanager，同时初始化self.hook值为self.pluginmanager.hook，这样Config对象就具备了pluggy的插件管理及hook能力，可通过Config对象.hook.hook函数

class Config:
    # ... 略

    def __init__(
        self,
        pluginmanager: PytestPluginManager,
        *,
        invocation_params: Optional[InvocationParams] = None,
    ) -> None:
        from .argparsing import Parser, FILE_OR_DIR

        if invocation_params is None:
            invocation_params = self.InvocationParams(
                args=(), plugins=None, dir=Path.cwd()
            )

        self.option = argparse.Namespace()
        """Access to command line option as attributes.

        :type: argparse.Namespace
        """

        self.invocation_params = invocation_params
        """The parameters with which pytest was invoked.

        :type: InvocationParams
        """

        _a = FILE_OR_DIR
        self._parser = Parser(
            usage=f"%(prog)s [options] [{_a}] [{_a}] [...]",
            processopt=self._processopt,
        )
        self.pluginmanager = pluginmanager # 增加插件管理器
        """The plugin manager handles plugin registration and hook invocation.

        :type: PytestPluginManager
        """

        self.trace = self.pluginmanager.trace.root.get("config")
        self.hook = self.pluginmanager.hook  # 增加hook属性
        self._inicache: Dict[str, Any] = {}
        self._override_ini: Sequence[str] = ()
        self._opt2dest: Dict[str, str] = {}
        self._cleanup: List[Callable[[], None]] = []
        # A place where plugins can store information on the config for their
        # own use. Currently only intended for internal plugins.
        self._store = Store()
        self.pluginmanager.register(self, "pytestconfig")
        self._configured = False
        self.hook.pytest_addoption.call_historic(
            kwargs=dict(parser=self._parser, pluginmanager=self.pluginmanager)
        )

        if TYPE_CHECKING:
            from _pytest.cacheprovider import Cache

            self.cache: Optional[Cache] = None

_pytest/config/__init__.py PytestPluginManager类

初始化时，通过self.add_hookspecs(_pytest.hookspec) 添加hook函数声明(接口)，同时通过self.register(self)把自己注册为插件实现;

import_plugin 中拼接_pytest/config/__init__.py中定义的模块，拼接后的形式，形如_pytest.python，然后导入并注册插件

@final
class PytestPluginManager(PluginManager):
    """A :py:class:`pluggy.PluginManager <pluggy.PluginManager>` with
    additional pytest-specific functionality:

    * Loading plugins from the command line, ``PYTEST_PLUGINS`` env variable and
      ``pytest_plugins`` global variables found in plugins being loaded.
    * ``conftest.py`` loading during start-up.
    """

    def __init__(self) -> None:
        import _pytest.assertion

        super().__init__("pytest")
        # The objects are module objects, only used generically.
        self._conftest_plugins: Set[types.ModuleType] = set()

        # State related to local conftest plugins.
        self._dirpath2confmods: Dict[Path, List[types.ModuleType]] = {}
        self._conftestpath2mod: Dict[Path, types.ModuleType] = {}
        self._confcutdir: Optional[Path] = None
        self._noconftest = False
        self._duplicatepaths: Set[Path] = set()

        # plugins that were explicitly skipped with pytest.skip
        # list of (module name, skip reason)
        # previously we would issue a warning when a plugin was skipped, but
        # since we refactored warnings as first citizens of Config, they are
        # just stored here to be used later.
        self.skipped_plugins: List[Tuple[str, str]] = []

        self.add_hookspecs(_pytest.hookspec)
        self.register(self)
        if os.environ.get("PYTEST_DEBUG"):
            err: IO[str] = sys.stderr
            encoding: str = getattr(err, "encoding", "utf8")
            try:
                err = open(
                    os.dup(err.fileno()),
                    mode=err.mode,
                    buffering=1,
                    encoding=encoding,
                )
            except Exception:
                pass
            self.trace.root.setwriter(err.write)
            self.enable_tracing()

        # Config._consider_importhook will set a real object if required.
        self.rewrite_hook = _pytest.assertion.DummyRewriteHook()
        # Used to know when we are importing conftests after the pytest_configure stage.
        self._configured = False

    def parse_hookimpl_opts(self, plugin: _PluggyPlugin, name: str):
        # pytest hooks are always prefixed with "pytest_",
        # so we avoid accessing possibly non-readable attributes
        # (see issue #1073).
        if not name.startswith("pytest_"):
            return
        # Ignore names which can not be hooks.
        if name == "pytest_plugins":
            return

        method = getattr(plugin, name)
        opts = super().parse_hookimpl_opts(plugin, name)

        # Consider only actual functions for hooks (#3775).
        if not inspect.isroutine(method):
            return

        # Collect unmarked hooks as long as they have the `pytest_' prefix.
        if opts is None and name.startswith("pytest_"):
            opts = {}
        if opts is not None:
            # TODO: DeprecationWarning, people should use hookimpl
            # https://github.com/pytest-dev/pytest/issues/4562
            known_marks = {m.name for m in getattr(method, "pytestmark", [])}

            for name in ("tryfirst", "trylast", "optionalhook", "hookwrapper"):
                opts.setdefault(name, hasattr(method, name) or name in known_marks)
        return opts

    def parse_hookspec_opts(self, module_or_class, name: str):
        opts = super().parse_hookspec_opts(module_or_class, name)
        if opts is None:
            method = getattr(module_or_class, name)

            if name.startswith("pytest_"):
                # todo: deprecate hookspec hacks
                # https://github.com/pytest-dev/pytest/issues/4562
                known_marks = {m.name for m in getattr(method, "pytestmark", [])}
                opts = {
                    "firstresult": hasattr(method, "firstresult")
                    or "firstresult" in known_marks,
                    "historic": hasattr(method, "historic")
                    or "historic" in known_marks,
                }
        return opts

    def register(
        self, plugin: _PluggyPlugin, name: Optional[str] = None
    ) -> Optional[str]:
        if name in _pytest.deprecated.DEPRECATED_EXTERNAL_PLUGINS:
            warnings.warn(
                PytestConfigWarning(
                    "{} plugin has been merged into the core, "
                    "please remove it from your requirements.".format(
                        name.replace("_", "-")
                    )
                )
            )
            return None
        ret: Optional[str] = super().register(plugin, name)
        if ret:
            self.hook.pytest_plugin_registered.call_historic(
                kwargs=dict(plugin=plugin, manager=self)
            )

            if isinstance(plugin, types.ModuleType):
                self.consider_module(plugin)
        return ret
        
     # ...略
     def import_plugin(self, modname: str, consider_entry_points: bool = False) -> None:
        """Import a plugin with ``modname``.

        If ``consider_entry_points`` is True, entry point names are also
        considered to find a plugin.
        """
        # Most often modname refers to builtin modules, e.g. "pytester",
        # "terminal" or "capture".  Those plugins are registered under their
        # basename for historic purposes but must be imported with the
        # _pytest prefix.
        assert isinstance(modname, str), (
            "module name as text required, got %r" % modname
        )
        if self.is_blocked(modname) or self.get_plugin(modname) is not None:
            return

        importspec = "_pytest." + modname if modname in builtin_plugins else modname
        self.rewrite_hook.mark_rewrite(importspec)

        if consider_entry_points:
            loaded = self.load_setuptools_entrypoints("pytest11", name=modname)
            if loaded:
                return

        try:
            __import__(importspec)
        except ImportError as e:
            raise ImportError(
                'Error importing plugin "{}": {}'.format(modname, str(e.args[0]))
            ).with_traceback(e.__traceback__) from e

        except Skipped as e:
            self.skipped_plugins.append((modname, e.msg or ""))
        else:
            mod = sys.modules[importspec]
            self.register(mod, modname)

这里重写了父类的register，如下，重写函数中也调用了父类的register函数

父类的register函数中，调用了self.parse_hookimpl_opts(plugin, name)，这个函数在当前类即PytestPluginManager类中重写了，所以，运行时调用的是重写后的PytestPluginManager.parse_hookimpl_opts(plugin, name)，该函数中，也会调用PluginManager.parse_hookimpl_opts函数，如果调用该父类函数获取返回值为None，并且函数名称以pytest__开头，则标记返回结果值为 {},这样PluginManager.register函数中，hookimpl_opts is not None表达式值为真，会继续往下执行代码，将没有使用hookimpl标记的，以pytest__打头的函数添加为对应hook函数的函数实现体。

pluggy/manage.py PluginManager类

class PluginManager(object):
    # ...略
    def register(self, plugin, name=None):
        """ Register a plugin and return its canonical name or None if the name
        is blocked from registering.  Raise a ValueError if the plugin is already
        registered. """

        plugin_name = name or self.get_canonical_name(plugin)

        if plugin_name in self._name2plugin or plugin in self._plugin2hookcallers:
            if self._name2plugin.get(plugin_name, -1) is None:
                return  # blocked plugin, return None to indicate no registration
            raise ValueError(
                "Plugin already registered: %s=%s
%s"
                % (plugin_name, plugin, self._name2plugin)
            )

        # XXX if an error happens we should make sure no state has been
        # changed at point of return
        self._name2plugin[plugin_name] = plugin

        # register matching hook implementations of the plugin
        self._plugin2hookcallers[plugin] = hookcallers = []

        for name in dir(plugin):
            hookimpl_opts = self.parse_hookimpl_opts(plugin, name) 
            if hookimpl_opts is not None:
                normalize_hookimpl_opts(hookimpl_opts)
                method = getattr(plugin, name)
                hookimpl = HookImpl(plugin, plugin_name, method, hookimpl_opts)
                hook = getattr(self.hook, name, None)
                if hook is None:
                    hook = _HookCaller(name, self._hookexec)
                    setattr(self.hook, name, hook)
                elif hook.has_spec():
                    self._verify_hook(hook, hookimpl)
                    hook._maybe_apply_history(hookimpl)
                hook._add_hookimpl(hookimpl)
                hookcallers.append(hook)
        return plugin_name

_pytest/config/__init__.py main函数定义

获取Config对象config后，通过调用config.hook.pytest_cmdline_main，从上到下，执行以下.py脚本中的pytest_cmdline_main函数

_pytest/setupplan.py
_pytest/setuponly.py
_pytest/mark/__init__.py
_pytest/cacheprovider.py
_python/python
_python/helpconfig
_python/main.py

_python/main.py

该文件中的 pytest_cmdline_main函数，负责执行测试

def pytest_cmdline_main(config):
    return wrap_session(config, _main)
    
def wrap_session(
    config: Config, doit: Callable[[Config, "Session"], Optional[Union[int, ExitCode]]]
) -> Union[int, ExitCode]:
    """Skeleton command line program"""
    session = Session.from_config(config)
    session.exitstatus = ExitCode.OK
    initstate = 0
    try:
        try:
            config._do_configure()
            initstate = 1
            config.hook.pytest_sessionstart(session=session)
            initstate = 2
            session.exitstatus = doit(config, session) or 0
        except UsageError:
            session.exitstatus = ExitCode.USAGE_ERROR
            raise
        except Failed:
            session.exitstatus = ExitCode.TESTS_FAILED
        except (KeyboardInterrupt, exit.Exception):
            excinfo = _pytest._code.ExceptionInfo.from_current()
            exitstatus = ExitCode.INTERRUPTED  # type: Union[int, ExitCode]
            if isinstance(excinfo.value, exit.Exception):
                if excinfo.value.returncode is not None:
                    exitstatus = excinfo.value.returncode
                if initstate < 2:
                    sys.stderr.write(
                        "{}: {}
".format(excinfo.typename, excinfo.value.msg)
                    )
            config.hook.pytest_keyboard_interrupt(excinfo=excinfo)
            session.exitstatus = exitstatus
        except:  # noqa
            session.exitstatus = ExitCode.INTERNAL_ERROR
            excinfo = _pytest._code.ExceptionInfo.from_current()
            try:
                config.notify_exception(excinfo, config.option)
            except exit.Exception as exc:
                if exc.returncode is not None:
                    session.exitstatus = exc.returncode
                sys.stderr.write("{}: {}
".format(type(exc).__name__, exc))
            else:
                if excinfo.errisinstance(SystemExit):
                    sys.stderr.write("mainloop: caught unexpected SystemExit!
")

    finally:
        # Explicitly break reference cycle.
        excinfo = None  # type: ignore
        session.startdir.chdir()
        if initstate >= 2:
            try:
                config.hook.pytest_sessionfinish(
                    session=session, exitstatus=session.exitstatus
                )
            except exit.Exception as exc:
                if exc.returncode is not None:
                    session.exitstatus = exc.returncode
                sys.stderr.write("{}: {}
".format(type(exc).__name__, exc))
        config._ensure_unconfigure()
    return session.exitstatus

def _main(config: Config, session: "Session") -> Optional[Union[int, ExitCode]]:
    """ default command line protocol for initialization, session,
    running tests and reporting. """
    config.hook.pytest_collection(session=session)
    config.hook.pytest_runtestloop(session=session)

    if session.testsfailed:
        return ExitCode.TESTS_FAILED
    elif session.testscollected == 0:
        return ExitCode.NO_TESTS_COLLECTED
    return None

def pytest_collection(session):
    return session.perform_collect()

def pytest_runtestloop(session):
    if session.testsfailed and not session.config.option.continue_on_collection_errors:
        raise session.Interrupted(
            "%d error%s during collection"
            % (session.testsfailed, "s" if session.testsfailed != 1 else "")
        )

    if session.config.option.collectonly:
        return True

    for i, item in enumerate(session.items): # session.items 获取值为为pytest测试脚本中的测试函数
        nextitem = session.items[i + 1] if i + 1 < len(session.items) else None
        item.config.hook.pytest_runtest_protocol(item=item, nextitem=nextitem)
        if session.shouldfail:
            raise session.Failed(session.shouldfail)
        if session.shouldstop:
            raise session.Interrupted(session.shouldstop)
    return True

item.config.hook.pytest_runtest_protocol执行顺序如下，从上到下执行各个脚本中对应的函数

pytest_runtest_protocol warnings.py
pytest_runtest_protocol assertion/__init__.py
pytest_runtest_protocol faulthandler
pytest_runtest_protocol unittest.py
pytest_runtest_protocol runner.py

_pytest/runner.py

pytest_runtest_protocol 负责执行pytest协议

def pytest_runtest_protocol(item, nextitem):
    item.ihook.pytest_runtest_logstart(nodeid=item.nodeid, location=item.location)
    runtestprotocol(item, nextitem=nextitem)
    item.ihook.pytest_runtest_logfinish(nodeid=item.nodeid, location=item.location)
    return True
    
def runtestprotocol(item, log=True, nextitem=None):
    hasrequest = hasattr(item, "_request")
    if hasrequest and not item._request:
        item._initrequest()
    rep = call_and_report(item, "setup", log)
    reports = [rep]
    if rep.passed:
        if item.config.getoption("setupshow", False):
            show_test_item(item)
        if not item.config.getoption("setuponly", False):
            reports.append(call_and_report(item, "call", log))
    reports.append(call_and_report(item, "teardown", log, nextitem=nextitem))
    # after all teardown hooks have been called
    # want funcargs and request info to go away
    if hasrequest:
        item._request = False
        item.funcargs = None
    return reports