xfail condition should include platform module in namespace

[jaraco]

One can currently write:

@pytest.xfail("sys.platform == 'darwin'")

But not

@pytest.xfail("platform.platform() == 'Darwin'")

If one tries that, an error is raised:

Error evaluating 'xfail' expression
    platform.platform() == "Darwin"
NameError: name 'platform' is not defined

It seems reasonable to me the platform module should be exposed in the namespace for these conditional methods for the same reason sys is.

I searched but could not find an existing issue or even a definition of what these conditional expressions are guaranteed to support, so I hope this is not a duplicate report.

[nicoddemus]

Definitely, thanks for the suggestion.

[nicoddemus]

This is a great first contribution, cc @feuillemorte.

[blueyed]

For what it's worth: I do not see the NameError when trying that (pytest
3.4.0):

==================================== test session starts ====================================
platform linux -- Python 3.6.4, pytest-3.3.3.dev15+g794fb193, py-1.5.2, pluggy-0.6.0
Using --randomly-seed=1519069598
Django settings: X.settings (from environment variable)
rootdir: …/project/project, inifile: setup.cfg
plugins: xdist-1.22.0, travis-fold-1.3.0, testmon-0.9.9, repeat-0.4.1, randomly-1.2.2, profiling-1.2.11, mock-1.6.3, forked-0.2, django-3.1.2, cov-2.5.1, asyncio-0.8.0, annotate-1.0.1, celery-4.1.0, pdb-0.3.0.dev0
collected 0 items / 1 errors                                                                

================================== short test summary info ==================================
ERROR tests/test_t.py
========================================== ERRORS ===========================================
_____________________________ ERROR collecting tests/test_t.py ______________________________
tests/test_t.py:4: in <module>
    @pytest.xfail("platform.platform() == 'Darwin'")
E   _pytest.outcomes.XFailed: platform.platform() == 'Darwin'
!!!!!!!!!!!!!!!!!!!!!!!!!! Interrupted: 1 errors during collection !!!!!!!!!!!!!!!!!!!!!!!!!!
================================== 1 error in 0.21 seconds ==================================

I wanted to try if @pytest.xfail("__import__('platform').platform() != 'Darwin'") could be used as a workaround, but the outcome is the same as above
for me.

[nicoddemus]

Now that I think about it, perhaps it uses the global namespace of the module of the test?

[svuki]

If I'm understanding correctly the problem isn't outcomes.xfail but the xfail mark which is talked about in the docs here.

If that's the case then the relevant code for what's available during evaluation of conditions is here:

pytest/_pytest/skipping.py

Lines 110 to 114 in bedceaa

	def _getglobals(self):
	d = {'os': os, 'sys': sys, 'config': self.item.config}
	if hasattr(self.item, 'obj'):
	d.update(self.item.obj.__globals__)
	return d

So it's the global namespace of the module of the test plus os, sys, and item.config.

[nicoddemus]

@svuki thanks for clarifying that! I believe we can just add platform to that initial directory in there then, I believe platform is as useful as sys.