TypeError in sandbox tests

[jaraco]

About a week ago, tests started failing like so with errors in hide_setuptools when module names are 'None'.

[jaraco]

I'm able to replicate the failures locally, but not against v28.8.0, so it appears to be a regression with some commit preceding the release of v28.9.0. The failure doesn't occur if I run tests with -k test_sandbox, so the failures seem to have some interaction with other tests.

[jaraco]

Well, I was able to replicate it locally, but now I'm not, even against master, and even when I run the whole test suite. I'm not sure what's going on.

[jaraco]

Running the test now, I'm getting the failure again. I think perhaps I hadn't properly gotten back to master.

I can replicate the test failure running only the tests from two files:

python -m tox -- -k 'test_sandbox or test_namespaces' 

[jaraco]

When it fails, there's a pseudo module in sys.modules[None]:

(Pdb) l
225  	    invocation to import the most appropriate setuptools. This technique is
226  	    necessary to avoid issues such as #315 where setuptools upgrading itself
227  	    would fail to find a function declared in the metadata.
228  	    """
229  	    modules = filter(_needs_hiding, sys.modules)
230  ->	    _clear_modules(modules)
231  	
232  	
233  	def run_setup(setup_script, args):
234  	    """Run a distutils setup script, sandboxed in its directory"""
235  	    setup_dir = os.path.abspath(os.path.dirname(setup_script))
(Pdb) sys.modules[None]
<module '_pycodecompile_pseudo_module' (1)>

[jaraco]

It appears to me that code is being injected by pytest here. It seems that code has been around a long time, so it's only now that it's been triggered, presumably by something in the new test_namespaces.py.

[jaraco]

If I remove the pytest skip, the issue doesn't occur.

$ git diff
diff --git a/setuptools/tests/test_namespaces.py b/setuptools/tests/test_namespaces.py
index 21fd69e..c148577 100644
--- a/setuptools/tests/test_namespaces.py
+++ b/setuptools/tests/test_namespaces.py
@@ -13,8 +13,6 @@ class TestNamespaces:
 
     @pytest.mark.xfail(sys.version_info < (3, 3),
         reason="Requires PEP 420")
-    @pytest.mark.skipif('os.environ.get("APPVEYOR")',
-        reason="https://github.com/pypa/setuptools/issues/851")
     def test_mixed_site_and_non_site(self, tmpdir):
         """
         Installing two packages sharing the same namespace, one installed
$ 

[jaraco]

That explains why the tests started failing recently -- that behavior was added in e8d53c0.

[jaraco]

Bypassing the string-style expression in the skip condition bypasses the issue, now reported upstream.