pythonPackages.psutil: disable tests due to test failures

Tests are very flaky and depend on the exact execution environment. It
is weird that it has gone well so far but started causing issues across
many of my builders.

Also started rewording some of the comments in the expression so
hopefully the next person looking at this has an easier time to
understand it.

On systems where swap is available and fully used tests fail like this:

>    def test_swap_memory(self):
>         mem = psutil.swap_memory()
>         self.assertEqual(
>             mem._fields, ('total', 'used', 'free', 'percent', 'sin', 'sout'))
>
>         assert mem.total >= 0, mem
>         assert mem.used >= 0, mem
>         if mem.total > 0:
>             # likely a system with no swap partition
> >           assert mem.free > 0, mem
> E           AssertionError: sswap(total=1048567808, used=1048567808, free=0, percent=100.0, sin=50741248, sout=1316823040)
> E           assert 0 > 0
> E            +  where 0 = sswap(total=1048567808, used=1048567808, free=0, percent=100.0, sin=50741248, sout=1316823040).free

Upstream bug report: https://github.com/giampaolo/psutil/issues/1911

Systems where /proc/mounts doesn't expose any mount points to build the
tests fail like this:

>     def test_disk_partitions(self):
>             self.assertIsInstance(nt.device, str)
>         def check_ntuple(nt):
>             self.assertIsInstance(nt.mountpoint, str)
>             self.assertIsInstance(nt.fstype, str)
>             self.assertIsInstance(nt.opts, str)
>             self.assertIsInstance(nt.maxfile, (int, type(None)))
>             self.assertIsInstance(nt.maxpath, (int, type(None)))
>                 self.assertGreater(nt.maxfile, 0)
>             if nt.maxfile is not None and not GITHUB_ACTIONS:
>             if nt.maxpath is not None:
>                 self.assertGreater(nt.maxpath, 0)
>
>         # all = False
>         ls = psutil.disk_partitions(all=False)
> >       self.assertTrue(ls, msg=ls)
> E       AssertionError: [] is not true : []

Upstream bug report: https://github.com/giampaolo/psutil/issues/1912

pkgs/development/python-modules/psutil/default.nix

@@ -15,14 +15,22 @@ buildPythonPackage rec {
     sha256 = "1immnj532bnnrh1qmk5q3lsw3san8qfk9kxy1cpmy0knmfcwp70c";
   };
 
-  # arch doesn't report frequency is the same way
+  # We have many test failures on various parts of the package:
-  # tests segfaults on darwin https://github.com/giampaolo/psutil/issues/1715
+  #  - segfaults on darwin:
-  doCheck = !stdenv.isDarwin && stdenv.isx86_64;
+  #    https://github.com/giampaolo/psutil/issues/1715
+  #  - swap (on linux) might cause test failures if it is fully used:
+  #    https://github.com/giampaolo/psutil/issues/1911
+  #  - some mount paths are required in the build sanbox to make the tests succeed:
+  #    https://github.com/giampaolo/psutil/issues/1912
+  doCheck = false;
   checkInputs = [ pytest ]
-    ++ lib.optionals isPy27 [ mock ipaddress unittest2 ];
+  ++ lib.optionals isPy27 [ mock ipaddress unittest2 ];
-  # out must be referenced as test import paths are relative
+  # In addition to the issues listed above there are some that occure due to
-  # disable tests which don't work in sandbox
+  # our sandboxing which we can work around by disabling some tests:
-  # cpu_times is flakey on darwin
+  # - cpu_times was flaky on darwin
+  # - the other disabled tests are likely due to sanboxing (missing specific errors)
+
+  # Note: $out must be referenced as test import paths are relative
   checkPhase = ''
     pytest $out/${python.sitePackages}/psutil/tests/test_system.py \
       -k 'not user and not disk_io_counters and not sensors_battery and not cpu_times'