I've noticed that on every call to datadir.__getitem__ the file is always "re-copied".

This is a problem in my opinion since my first impression of calling __getitem__ is that only the path of the file is returned, not copied again.

Request

Add some sort of structure that incorporates data files in a subdirectory that aren't explicit name matches for a test file.

Issue Description

Often when projects get large you want to start using subdirectories in your project. You don't really want to share data between all of your test modules but you do want a subset of your test files to share the same data.

Example Test Structure

I want to share data files for all files in performance_stats.

test/
├── data
├── dict_types_unit_test.py
├── __init__.py
├── performance_stats
│   ├── 20181018_runlog.txt # Test Data
│   ├── 20181019_runlog.txt # Test Data
│   ├── fixtures.pyc
│   ├── __init__.py
│   ├── integration_tests.py
│   ├── test_cli.py
│   └── test_parsing.py
├── setz_unit_test.py
├── test-report.xml
└── yaml_config_base_unit_test.py

Current Work Around

use shared_datadir and accept a "global" namespace.

Unimportant note

I appreciate the library a lot. I've been writing my own fixtures to do this for years. =D

I just noticed that we set the Development Status to Production, but have not released 1.0 yet. My question is:

@gabrielcnr do you see still think the API might change? If so, we should probably change the Development Status to Alpha or Beta. If not, we should probably release 1.0 and promise backward compatibility, at least until 2.0 is released.

Hi, it seems that the plugin fixtures' default scope is function, when I try to reference the fixture from a fixture with session scope, py.test will raise a ScopeMismatch error.

My use case is:

1. put a database schema init sql file to the data dir
2. add a fixture call init_db, which has session scope, and it will recreate the database schema only once during the whole test execution
3. init_db fixture use shared_datadir to read the init sql file

Any suggestions for this use case? Or can we change the plugin fixtures scope to session (or something else)?

Just a suggestion, I'm always had a little bit of work to update files in the shared data dirs. Do you think in a way to update files?

I used sometimes jest with snapshots it has a very good way to update snapshot files. Maybe we could implement something in this way, what do you think? https://jestjs.io/docs/en/snapshot-testing#updating-snapshots

Tks!!

@gabrielcnr

I don't have access, so you will need to first enable Travis on this repository. Go to travis.org, go into "My Repositories" on the top left and flip the switch for pytest-datadir. :grin:

I enabled it for my fork, you can see the first build here.

Unfortunately LGPL brings a number of problems for some people/organizations:

From pytest-dev/pytest-mock#45:

I can't use any form of GPL at work (including LGPL). Even if it was possible, the handling considerations wouldn't be worth it for a plugin. A few months ago I had a remote worker try to borrow code from an LGPL plugin for a project, thinking "hey it's open source, and freedom". Its not easy to convey the ramification of creating a derivative work.

pytest itself is MIT.

What do you think about changing the license of this plugin to MIT?

This adds a second lookup place for data files at the 'data' dir from the tests folder. With this, tests can share the same data files over different modules but still able to have their own files, who will take precedence over the global 'data' dir. This also improves the docs with usage info and provides a tox.ini to test in py27 and py34

updates:

• https://github.com/myint/autoflake → https://github.com/PyCQA/autoflake
• github.com/PyCQA/autoflake: v1.5.3 → v1.6.0
• https://gitlab.com/pycqa/flake8 → https://github.com/PyCQA/flake8
• github.com/PyCQA/flake8: 3.9.2 → 5.0.4

updates:

• github.com/PyCQA/autoflake: v1.7.7 → v2.0.0
• github.com/psf/black: 22.10.0 → 22.12.0
• github.com/pre-commit/pre-commit-hooks: v4.3.0 → v4.4.0
• github.com/PyCQA/flake8: 5.0.4 → 6.0.0

Thank you very much for the plugin Have you considered including a test_method_dir (or a similar name) to be able to have files only for one method (instead of the whole module)? I don't think it's a good idea to copy all the files in a module when I only want the files for one method. The directory for the method would be inside the module directory. In the example, it would be test_hello \ test_a_method, so I could inject what is common to the module or what is necessary only for the method. If you give the OK, I could try to do it myself and do a PR. Thanks.

Just normal build, install and test cycle used on building package from non-root account:

• "setup.py build"
• "setup.py install --root </install/prefix>"
• "pytest with PYTHONPATH pointing to setearch and sitelib inside </install/prefix>

+ PYTHONPATH=/home/tkloczko/rpmbuild/BUILDROOT/python-pytest-datadir-1.3.1-2.fc35.x86_64/usr/lib64/python3.8/site-packages:/home/tkloczko/rpmbuild/BUILDROOT/python-pytest-datadir-1.3.1-2.fc35.x86_64/usr/lib/python3.8/site-packages
+ PYTHONDONTWRITEBYTECODE=1
+ /usr/bin/pytest -ra
=========================================================================== test session starts ============================================================================
platform linux -- Python 3.8.9, pytest-6.2.4, py-1.10.0, pluggy-0.13.1
benchmark: 3.4.1 (defaults: timer=time.perf_counter disable_gc=False min_rounds=5 min_time=0.000005 max_time=1.0 calibration_precision=10 warmup=False warmup_iterations=100000)
Using --randomly-seed=1916038535
rootdir: /home/tkloczko/rpmbuild/BUILD/pytest-datadir-1.3.1
plugins: datadir-1.3.1, forked-1.3.0, shutil-1.7.0, virtualenv-1.7.0, expect-1.1.0, httpbin-1.0.0, flake8-1.0.7, timeout-1.4.2, betamax-0.8.1, freezegun-0.4.2, case-1.5.3, isort-1.3.0, aspectlib-1.5.2, asyncio-0.15.1, toolbox-0.5, xprocess-0.17.1, aiohttp-0.3.0, checkdocs-2.7.0, mock-3.6.1, rerunfailures-9.1.1, requests-mock-1.9.3, cov-2.12.1, pyfakefs-4.5.0, cases-3.6.1, flaky-3.7.0, hypothesis-6.14.0, benchmark-3.4.1, xdist-2.3.0, pylama-7.7.1, randomly-3.8.0, Faker-8.8.2
collected 10 items

. F                                                                                                                                                                  [ 11%]
tests/test_hello.py ......                                                                                                                                           [ 77%]
tests/test_pathlib.py s                                                                                                                                              [ 88%]
tests/test_nonexistent.py .                                                                                                                                          [100%]

================================================================================= FAILURES =================================================================================
_______________________________________________________________________________ test session _______________________________________________________________________________

cls = <class '_pytest.runner.CallInfo'>, func = <function call_runtest_hook.<locals>.<lambda> at 0x7fa6f5ad89d0>, when = 'call'
reraise = (<class '_pytest.outcomes.Exit'>, <class 'KeyboardInterrupt'>)

    @classmethod
    def from_call(
        cls,
        func: "Callable[[], TResult]",
        when: "Literal['collect', 'setup', 'call', 'teardown']",
        reraise: Optional[
            Union[Type[BaseException], Tuple[Type[BaseException], ...]]
        ] = None,
    ) -> "CallInfo[TResult]":
        excinfo = None
        start = timing.time()
        precise_start = timing.perf_counter()
        try:
>           result: Optional[TResult] = func()

/usr/lib/python3.8/site-packages/_pytest/runner.py:311:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

>       lambda: ihook(item=item, **kwds), when=when, reraise=reraise
    )

/usr/lib/python3.8/site-packages/_pytest/runner.py:255:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

self = <_HookCaller 'pytest_runtest_call'>, args = (), kwargs = {'item': <CheckdocsItem project>}, notincall = set()

    def __call__(self, *args, **kwargs):
        if args:
            raise TypeError("hook calling supports only keyword arguments")
        assert not self.is_historic()
        if self.spec and self.spec.argnames:
            notincall = (
                set(self.spec.argnames) - set(["__multicall__"]) - set(kwargs.keys())
            )
            if notincall:
                warnings.warn(
                    "Argument(s) {} which are declared in the hookspec "
                    "can not be found in this hook call".format(tuple(notincall)),
                    stacklevel=2,
                )
>       return self._hookexec(self, self.get_hookimpls(), kwargs)

/usr/lib/python3.8/site-packages/pluggy/hooks.py:286:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

self = <_pytest.config.PytestPluginManager object at 0x7fa6fd062f10>, hook = <_HookCaller 'pytest_runtest_call'>
methods = [<HookImpl plugin_name='runner', plugin=<module '_pytest.runner' from '/usr/lib/python3.8/site-packages/_pytest/runner...pper name='/dev/null' mode='r' encoding='UTF-8'>> _state='suspended' _in_suspended=False> _capture_fixture=None>>, ...]
kwargs = {'item': <CheckdocsItem project>}

    def _hookexec(self, hook, methods, kwargs):
        # called from all hookcaller instances.
        # enable_tracing will set its own wrapping function at self._inner_hookexec
>       return self._inner_hookexec(hook, methods, kwargs)

/usr/lib/python3.8/site-packages/pluggy/manager.py:93:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

hook = <_HookCaller 'pytest_runtest_call'>
methods = [<HookImpl plugin_name='runner', plugin=<module '_pytest.runner' from '/usr/lib/python3.8/site-packages/_pytest/runner...pper name='/dev/null' mode='r' encoding='UTF-8'>> _state='suspended' _in_suspended=False> _capture_fixture=None>>, ...]
kwargs = {'item': <CheckdocsItem project>}

>   self._inner_hookexec = lambda hook, methods, kwargs: hook.multicall(
        methods,
        kwargs,
        firstresult=hook.spec.opts.get("firstresult") if hook.spec else False,
    )

/usr/lib/python3.8/site-packages/pluggy/manager.py:84:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

hook_impls = [<HookImpl plugin_name='runner', plugin=<module '_pytest.runner' from '/usr/lib/python3.8/site-packages/_pytest/runner...pper name='/dev/null' mode='r' encoding='UTF-8'>> _state='suspended' _in_suspended=False> _capture_fixture=None>>, ...]
caller_kwargs = {'item': <CheckdocsItem project>}, firstresult = False

    def _multicall(hook_impls, caller_kwargs, firstresult=False):
        """Execute a call into multiple python functions/methods and return the
        result(s).

        ``caller_kwargs`` comes from _HookCaller.__call__().
        """
        __tracebackhide__ = True
        results = []
        excinfo = None
        try:  # run impl and wrapper setup functions in a loop
            teardowns = []
            try:
                for hook_impl in reversed(hook_impls):
                    try:
                        args = [caller_kwargs[argname] for argname in hook_impl.argnames]
                    except KeyError:
                        for argname in hook_impl.argnames:
                            if argname not in caller_kwargs:
                                raise HookCallError(
                                    "hook call must provide argument %r" % (argname,)
                                )

                    if hook_impl.hookwrapper:
                        try:
                            gen = hook_impl.function(*args)
                            next(gen)  # first yield
                            teardowns.append(gen)
                        except StopIteration:
                            _raise_wrapfail(gen, "did not yield")
                    else:
                        res = hook_impl.function(*args)
                        if res is not None:
                            results.append(res)
                            if firstresult:  # halt further impl calls
                                break
            except BaseException:
                excinfo = sys.exc_info()
        finally:
            if firstresult:  # first result hooks return a single value
                outcome = _Result(results[0] if results else None, excinfo)
            else:
                outcome = _Result(results, excinfo)

            # run all wrapper post-yield blocks
            for gen in reversed(teardowns):
                try:
                    gen.send(outcome)
                    _raise_wrapfail(gen, "has second yield")
                except StopIteration:
                    pass

>           return outcome.get_result()

/usr/lib/python3.8/site-packages/pluggy/callers.py:208:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

self = <pluggy.callers._Result object at 0x7fa6f5aaea60>

    def get_result(self):
        """Get the result(s) for this hook call.

        If the hook was marked as a ``firstresult`` only a single value
        will be returned otherwise a list of results.
        """
        __tracebackhide__ = True
        if self._excinfo is None:
            return self._result
        else:
            ex = self._excinfo
            if _py3:
>               raise ex[1].with_traceback(ex[2])

/usr/lib/python3.8/site-packages/pluggy/callers.py:80:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

hook_impls = [<HookImpl plugin_name='runner', plugin=<module '_pytest.runner' from '/usr/lib/python3.8/site-packages/_pytest/runner...pper name='/dev/null' mode='r' encoding='UTF-8'>> _state='suspended' _in_suspended=False> _capture_fixture=None>>, ...]
caller_kwargs = {'item': <CheckdocsItem project>}, firstresult = False

    def _multicall(hook_impls, caller_kwargs, firstresult=False):
        """Execute a call into multiple python functions/methods and return the
        result(s).

        ``caller_kwargs`` comes from _HookCaller.__call__().
        """
        __tracebackhide__ = True
        results = []
        excinfo = None
        try:  # run impl and wrapper setup functions in a loop
            teardowns = []
            try:
                for hook_impl in reversed(hook_impls):
                    try:
                        args = [caller_kwargs[argname] for argname in hook_impl.argnames]
                    except KeyError:
                        for argname in hook_impl.argnames:
                            if argname not in caller_kwargs:
                                raise HookCallError(
                                    "hook call must provide argument %r" % (argname,)
                                )

                    if hook_impl.hookwrapper:
                        try:
                            gen = hook_impl.function(*args)
                            next(gen)  # first yield
                            teardowns.append(gen)
                        except StopIteration:
                            _raise_wrapfail(gen, "did not yield")
                    else:
>                       res = hook_impl.function(*args)

/usr/lib/python3.8/site-packages/pluggy/callers.py:187:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

item = <CheckdocsItem project>

    def pytest_runtest_call(item: Item) -> None:
        _update_current_test_var(item, "call")
        try:
            del sys.last_type
            del sys.last_value
            del sys.last_traceback
        except AttributeError:
            pass
        try:
            item.runtest()
        except Exception as e:
            # Store trace info to allow postmortem debugging
            sys.last_type = type(e)
            sys.last_value = e
            assert e.__traceback__ is not None
            # Skip *this* frame
            sys.last_traceback = e.__traceback__.tb_next
>           raise e

/usr/lib/python3.8/site-packages/_pytest/runner.py:170:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

item = <CheckdocsItem project>

    def pytest_runtest_call(item: Item) -> None:
        _update_current_test_var(item, "call")
        try:
            del sys.last_type
            del sys.last_value
            del sys.last_traceback
        except AttributeError:
            pass
        try:
>           item.runtest()

/usr/lib/python3.8/site-packages/_pytest/runner.py:162:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

self = <CheckdocsItem project>

    def runtest(self):
>       desc = self.get_long_description()

/usr/lib/python3.8/site-packages/pytest_checkdocs/__init__.py:29:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

self = <CheckdocsItem project>

    def get_long_description(self):
>       return Description.from_md(ensure_clean(pep517.meta.load('.').metadata))

/usr/lib/python3.8/site-packages/pytest_checkdocs/__init__.py:60:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

root = '.'

    def load(root):
        """
        Given a source directory (root) of a package,
        return an importlib.metadata.Distribution object
        with metadata build from that package.
        """
        root = os.path.expanduser(root)
        system = compat_system(root)
        builder = functools.partial(build, source_dir=root, system=system)
>       path = Path(build_as_zip(builder))

/usr/lib/python3.8/site-packages/pep517/meta.py:71:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

builder = functools.partial(<function build at 0x7fa6fa00baf0>, source_dir='.', system={'build-backend': 'setuptools.build_meta:__legacy__', 'requires': ['setuptools', 'wheel']})

    def build_as_zip(builder=build):
        with tempdir() as out_dir:
>           builder(dest=out_dir)

/usr/lib/python3.8/site-packages/pep517/meta.py:58:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

source_dir = '.', dest = '/tmp/tmps6v8iqcl', system = {'build-backend': 'setuptools.build_meta:__legacy__', 'requires': ['setuptools', 'wheel']}

    def build(source_dir='.', dest=None, system=None):
        system = system or load_system(source_dir)
        dest = os.path.join(source_dir, dest or 'dist')
        mkdir_p(dest)
        validate_system(system)
        hooks = Pep517HookCaller(
            source_dir, system['build-backend'], system.get('backend-path')
        )

        with hooks.subprocess_runner(quiet_subprocess_runner):
            with BuildEnvironment() as env:
                env.pip_install(system['requires'])
>               _prep_meta(hooks, env, dest)

/usr/lib/python3.8/site-packages/pep517/meta.py:53:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

hooks = <pep517.wrappers.Pep517HookCaller object at 0x7fa6f5b15460>, env = <pep517.envbuild.BuildEnvironment object at 0x7fa6f5b15d30>, dest = '/tmp/tmps6v8iqcl'

    def _prep_meta(hooks, env, dest):
        reqs = hooks.get_requires_for_build_wheel({})
        log.info('Got build requires: %s', reqs)

        env.pip_install(reqs)
        log.info('Installed dynamic build dependencies')

        with tempdir() as td:
            log.info('Trying to build metadata in %s', td)
>           filename = hooks.prepare_metadata_for_build_wheel(td, {})

/usr/lib/python3.8/site-packages/pep517/meta.py:36:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

self = <pep517.wrappers.Pep517HookCaller object at 0x7fa6f5b15460>, metadata_directory = '/tmp/tmphqw_z7w2', config_settings = {}, _allow_fallback = True

    def prepare_metadata_for_build_wheel(
            self, metadata_directory, config_settings=None,
            _allow_fallback=True):
        """Prepare a ``*.dist-info`` folder with metadata for this project.

        Returns the name of the newly created folder.

        If the build backend defines a hook with this name, it will be called
        in a subprocess. If not, the backend will be asked to build a wheel,
        and the dist-info extracted from that (unless _allow_fallback is
        False).
        """
>       return self._call_hook('prepare_metadata_for_build_wheel', {
            'metadata_directory': abspath(metadata_directory),
            'config_settings': config_settings,
            '_allow_fallback': _allow_fallback,
        })

/usr/lib/python3.8/site-packages/pep517/wrappers.py:184:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

self = <pep517.wrappers.Pep517HookCaller object at 0x7fa6f5b15460>, hook_name = 'prepare_metadata_for_build_wheel'
kwargs = {'_allow_fallback': True, 'config_settings': {}, 'metadata_directory': '/tmp/tmphqw_z7w2'}

    def _call_hook(self, hook_name, kwargs):
        # On Python 2, pytoml returns Unicode values (which is correct) but the
        # environment passed to check_call needs to contain string values. We
        # convert here by encoding using ASCII (the backend can only contain
        # letters, digits and _, . and : characters, and will be used as a
        # Python identifier, so non-ASCII content is wrong on Python 2 in
        # any case).
        # For backend_path, we use sys.getfilesystemencoding.
        if sys.version_info[0] == 2:
            build_backend = self.build_backend.encode('ASCII')
        else:
            build_backend = self.build_backend
        extra_environ = {'PEP517_BUILD_BACKEND': build_backend}

        if self.backend_path:
            backend_path = os.pathsep.join(self.backend_path)
            if sys.version_info[0] == 2:
                backend_path = backend_path.encode(sys.getfilesystemencoding())
            extra_environ['PEP517_BACKEND_PATH'] = backend_path

        with tempdir() as td:
            hook_input = {'kwargs': kwargs}
            compat.write_json(hook_input, pjoin(td, 'input.json'),
                              indent=2)

            # Run the hook in a subprocess
            with _in_proc_script_path() as script:
                python = self.python_executable
>               self._subprocess_runner(
                    [python, abspath(str(script)), hook_name, td],
                    cwd=self.source_dir,
                    extra_environ=extra_environ
                )

/usr/lib/python3.8/site-packages/pep517/wrappers.py:265:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

cmd = ['/usr/bin/python3', '/usr/lib/python3.8/site-packages/pep517/in_process/_in_process.py', 'prepare_metadata_for_build_wheel', '/tmp/tmp442xzl4j']
cwd = '/home/tkloczko/rpmbuild/BUILD/pytest-datadir-1.3.1', extra_environ = {'PEP517_BUILD_BACKEND': 'setuptools.build_meta:__legacy__'}

    def quiet_subprocess_runner(cmd, cwd=None, extra_environ=None):
        """A method of calling the wrapper subprocess while suppressing output."""
        env = os.environ.copy()
        if extra_environ:
            env.update(extra_environ)

>       check_output(cmd, cwd=cwd, env=env, stderr=STDOUT)

/usr/lib/python3.8/site-packages/pep517/wrappers.py:75:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

timeout = None
popenargs = (['/usr/bin/python3', '/usr/lib/python3.8/site-packages/pep517/in_process/_in_process.py', 'prepare_metadata_for_build_wheel', '/tmp/tmp442xzl4j'],)
kwargs = {'cwd': '/home/tkloczko/rpmbuild/BUILD/pytest-datadir-1.3.1', 'env': {'AR': '/usr/bin/gcc-ar', 'BASH_FUNC_which%%': '(...sh-protection -fcf-protection -fdata-sections -ffunction-sections -flto=auto -flto-partition=none', ...}, 'stderr': -2}

    def check_output(*popenargs, timeout=None, **kwargs):
        r"""Run command with arguments and return its output.

        If the exit code was non-zero it raises a CalledProcessError.  The
        CalledProcessError object will have the return code in the returncode
        attribute and output in the output attribute.

        The arguments are the same as for the Popen constructor.  Example:

        >>> check_output(["ls", "-l", "/dev/null"])
        b'crw-rw-rw- 1 root root 1, 3 Oct 18  2007 /dev/null\n'

        The stdout argument is not allowed as it is used internally.
        To capture standard error in the result, use stderr=STDOUT.

        >>> check_output(["/bin/sh", "-c",
        ...               "ls -l non_existent_file ; exit 0"],
        ...              stderr=STDOUT)
        b'ls: non_existent_file: No such file or directory\n'

        There is an additional optional argument, "input", allowing you to
        pass a string to the subprocess's stdin.  If you use this argument
        you may not also use the Popen constructor's "stdin" argument, as
        it too will be used internally.  Example:

        >>> check_output(["sed", "-e", "s/foo/bar/"],
        ...              input=b"when in the course of fooman events\n")
        b'when in the course of barman events\n'

        By default, all communication is in bytes, and therefore any "input"
        should be bytes, and the return value will be bytes.  If in text mode,
        any "input" should be a string, and the return value will be a string
        decoded according to locale encoding, or by "encoding" if set. Text mode
        is triggered by setting any of text, encoding, errors or universal_newlines.
        """
        if 'stdout' in kwargs:
            raise ValueError('stdout argument not allowed, it will be overridden.')

        if 'input' in kwargs and kwargs['input'] is None:
            # Explicitly passing input=None was previously equivalent to passing an
            # empty string. That is maintained here for backwards compatibility.
            if kwargs.get('universal_newlines') or kwargs.get('text'):
                empty = ''
            else:
                empty = b''
            kwargs['input'] = empty

>       return run(*popenargs, stdout=PIPE, timeout=timeout, check=True,
                   **kwargs).stdout

/usr/lib64/python3.8/subprocess.py:415:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

input = None, capture_output = False, timeout = None, check = True
popenargs = (['/usr/bin/python3', '/usr/lib/python3.8/site-packages/pep517/in_process/_in_process.py', 'prepare_metadata_for_build_wheel', '/tmp/tmp442xzl4j'],)
kwargs = {'cwd': '/home/tkloczko/rpmbuild/BUILD/pytest-datadir-1.3.1', 'env': {'AR': '/usr/bin/gcc-ar', 'BASH_FUNC_which%%': '(...-fcf-protection -fdata-sections -ffunction-sections -flto=auto -flto-partition=none', ...}, 'stderr': -2, 'stdout': -1}
process = <subprocess.Popen object at 0x7fa6f5aae4f0>
stdout = b'Traceback (most recent call last):\n  File "/usr/lib/python3.8/site-packages/pep517/in_process/_in_process.py", line...ng pip, instead of https://github.com/user/proj/archive/master.zip use git+https://github.com/user/proj.git#egg=proj\n'
stderr = None, retcode = 1

    def run(*popenargs,
            input=None, capture_output=False, timeout=None, check=False, **kwargs):
        """Run command with arguments and return a CompletedProcess instance.

        The returned instance will have attributes args, returncode, stdout and
        stderr. By default, stdout and stderr are not captured, and those attributes
        will be None. Pass stdout=PIPE and/or stderr=PIPE in order to capture them.

        If check is True and the exit code was non-zero, it raises a
        CalledProcessError. The CalledProcessError object will have the return code
        in the returncode attribute, and output & stderr attributes if those streams
        were captured.

        If timeout is given, and the process takes too long, a TimeoutExpired
        exception will be raised.

        There is an optional argument "input", allowing you to
        pass bytes or a string to the subprocess's stdin.  If you use this argument
        you may not also use the Popen constructor's "stdin" argument, as
        it will be used internally.

        By default, all communication is in bytes, and therefore any "input" should
        be bytes, and the stdout and stderr will be bytes. If in text mode, any
        "input" should be a string, and stdout and stderr will be strings decoded
        according to locale encoding, or by "encoding" if set. Text mode is
        triggered by setting any of text, encoding, errors or universal_newlines.

        The other arguments are the same as for the Popen constructor.
        """
        if input is not None:
            if kwargs.get('stdin') is not None:
                raise ValueError('stdin and input arguments may not both be used.')
            kwargs['stdin'] = PIPE

        if capture_output:
            if kwargs.get('stdout') is not None or kwargs.get('stderr') is not None:
                raise ValueError('stdout and stderr arguments may not be used '
                                 'with capture_output.')
            kwargs['stdout'] = PIPE
            kwargs['stderr'] = PIPE

        with Popen(*popenargs, **kwargs) as process:
            try:
                stdout, stderr = process.communicate(input, timeout=timeout)
            except TimeoutExpired as exc:
                process.kill()
                if _mswindows:
                    # Windows accumulates the output in a single blocking
                    # read() call run on child threads, with the timeout
                    # being done in a join() on those threads.  communicate()
                    # _after_ kill() is required to collect that and add it
                    # to the exception.
                    exc.stdout, exc.stderr = process.communicate()
                else:
                    # POSIX _communicate already populated the output so
                    # far into the TimeoutExpired exception.
                    process.wait()
                raise
            except:  # Including KeyboardInterrupt, communicate handled that.
                process.kill()
                # We don't call process.wait() as .__exit__ does that for us.
                raise
            retcode = process.poll()
            if check and retcode:
>               raise CalledProcessError(retcode, process.args,
                                         output=stdout, stderr=stderr)
E               subprocess.CalledProcessError: Command '['/usr/bin/python3', '/usr/lib/python3.8/site-packages/pep517/in_process/_in_process.py', 'prepare_metadata_for_build_wheel', '/tmp/tmp442xzl4j']' returned non-zero exit status 1.

/usr/lib64/python3.8/subprocess.py:516: CalledProcessError
========================================================================= short test summary info ==========================================================================
SKIPPED [1] tests/test_pathlib.py:4: Python 2 only
FAILED ::project - subprocess.CalledProcessError: Command '['/usr/bin/python3', '/usr/lib/python3.8/site-packages/pep517/in_process/_in_process.py', 'prepare_metadata_fo...
================================================================== 1 failed, 7 passed, 1 skipped in 8.04s ==================================================================

Pytest is reporting OSError with even trivial test case below:

C:\Users\foobar\repo> type tests\test_datadir.py

def test_datadir(shared_datadir):
    assert True

Gist link for error log here.

It happens only when following requirements are all met:

1. datadir or shared_datadir is actually used in test case, even only as function argument. Tests not using these fixtures at all would be fine.
2. Windows temp path is using RAM disk, not normal drives attached to physical storage

For second point, above test case would succeed if pytest is instructed to use normal drive as temp, like:

pytest --basetemp=C:\Temp -k test_datadir -s tests\

As extra info, here is my RAM drive setup (if it is useful at all):

C:\Users\foobar\repo> imdisk.exe -l -u 0
Drive letter: M
Image file: \BaseNamedObjects\Global\RamDyne8694d353
Size: 12884901888 bytes (12 GB), Proxy, HDD, Modified.

C:\Users\foobar\repo> echo %TEMP%
M:\Temp

The issue pytest-dev/pytest#5826 has symptom very similar to this one, which ultimately points to long time unfixed python bug in Path.resolve(). Comment in Python bug 33016 also has some insight about resolve() being unable to handle Windows filesystem API properly.

While it may not be the responsibility for pytest-datadir to handle such failure, how about some warning ahead. such as in README, for similar user case? Because the bug doesn't manifest unless datadir plugin is installed and used, people may come search here for solution initially. Not to mention the real bug won't go away anytime soon...

I have, due to DFS in my environment, tests running in a dfs path, which results in a UNC path (\\my.domain\dfs\some\path) being passed to copytree in shared_datadir(). This results in copytree failing with

OSError: [WinError 123] The filename, directory name, or volume label syntax is incorrect: '\\\\?\\\\\\my.domain\\dfs\\bla...

I traced this back to return '\\\\?\\' + os.path.normpath(path) in plugin._win32_longpath(), which afaict is not correct in case of a UNC path (see above UNC link). Then you need to insert an additional UNC\, so the prefix should be '\\\\?\\UNC\\' instead. UNC paths should be recognizable because they start with \\.