PYTEST_CURRENT_TEST explodes on windows where the env var limit is 32767 bytes

[jonathanunderwood]

• Include a detailed description of the bug or suggestion
• pip list of the virtual environment you are using
• pytest and operating system versions
• Minimal example if possible

I have a fixture defined like this:

@pytest.fixture(
    params=[
        (b''),
        (os.urandom(32 * 1024)),
        (b'0' * 1024),
    ]
)
def data(request):
    return request.param

This causes problems on Windows whenever a test uses that fixture, because pytest tries to stuff the parameter values into PYTEST_CURRENT_TEST, and the value of data is large such that the PYTEST_CURRENT_TEST env var would end up being larger than the maximum allowed size on windows (32767 bytes). Here's an example failure (on appveyor):

self = {'APPVEYOR_REPO_COMMIT_AUTHOR': 'Jonathan Underwood', 'VS100COMNTOOLS': 'c:\\Program Files (x86)\\Microsoft Visual Stu...C:\\Program Files (x86)\\Microsoft DirectX SDK (June 2010)\\', 'COMMONPROGRAMW6432': 'C:\\Program Files\\Common Files'}
key = 'PYTEST_CURRENT_TEST'
item = 'tests/test_block.py::test_threads2[e\\x17\\xcfK\\x9f\\xb3rw\\x82\\x1a\\x14\\xf1Wc\\xf9\\x99S\\xf6\\x1b\\xcd\\xe0,\\x8...\xc3\\xdeT\\x19\\xe4l\\xeeH\\xbd\\xba\\x1b\\xd3\\xaf\\x02\\xeb\\xfe\\xf4\\xc9\\xa7pA\\xc3I-mode11-store_size0] (setup)'
    def __setitem__(self, key, item):
>       putenv(key, item)
E       ValueError: the environment variable is longer than 32767 bytes

I think what's needed is some way of saying to pytest "use this alias for this parameter value when composing PYTEST_CURRENT_TEST", or "don't set PYTEST_CURRENT_TEST".

[RonnyPfannschmidt]

@jonathanunderwood pytest.param(os.urandom(32 * 1024), id='random:32KB') should work

@nicoddemus i believe its a bug that we simply escape random binary data - we really should use a auto-id there at least

[jonathanunderwood]

Thanks - can confirm that setting ids fixes the immediate issue. It would be great for users if this was handled more gracefully by pytest. Some things spring to mind:

• catch the exception and truncate PYTEST_CURRENT_TEST, possibly testing for if it's running on windows (which has a short env var length than linux etc)
• autogenerate ids for all parameters for which ids aren't specified eg. using the fixture name and a counter
• Allow users to specify that PYTEST_CURRENT_TEST should not be generated with a command line flag

[RonnyPfannschmidt]

@jonathanunderwood

altering the id on the exception is not possible as its set in stone bytheon

auto-generating the ids is what should happen, however in order to ensure better test id comprehension we do try to use a text representation if sensible, the case you are hitting is where we use a string representation where it is certainly not sensible

i have no opinion on adding a option/flag for this - i defer to @nicoddemus on that one

[The-Compiler]

Duplicate of #6881 (closing this one because the other already has a PR associated with it)