Revert change to test skip condition

This was part of a commit cherry picked from another branch, and this
change didn't make sense on this branch.

IPython/kernel/tests/test_kernelspec.py

@@ -1,66 +1,64 b''
 import json
 import os
 from os.path import join as pjoin
 import unittest
 
 from IPython.testing.decorators import onlyif
 from IPython.utils.tempdir import TemporaryDirectory
 from IPython.kernel import kernelspec
 
 sample_kernel_json = {'argv':['cat', '{connection_file}'],
                       'display_name':'Test kernel',
                      }
 
 class KernelSpecTests(unittest.TestCase):
     def setUp(self):
         td = TemporaryDirectory()
         self.addCleanup(td.cleanup)
         self.sample_kernel_dir = pjoin(td.name, 'kernels', 'Sample')
         os.makedirs(self.sample_kernel_dir)
         json_file = pjoin(self.sample_kernel_dir, 'kernel.json')
         with open(json_file, 'w') as f:
             json.dump(sample_kernel_json, f)
 
         self.ksm = kernelspec.KernelSpecManager(ipython_dir=td.name)
         
         td2 = TemporaryDirectory()
         self.addCleanup(td2.cleanup)
         self.installable_kernel = td2.name
         with open(pjoin(self.installable_kernel, 'kernel.json'), 'w') as f:
             json.dump(sample_kernel_json, f)
 
     def test_find_kernel_specs(self):
         kernels = self.ksm.find_kernel_specs()
         self.assertEqual(kernels['sample'], self.sample_kernel_dir)
 
     def test_get_kernel_spec(self):
         ks = self.ksm.get_kernel_spec('SAMPLE')  # Case insensitive
         self.assertEqual(ks.resource_dir, self.sample_kernel_dir)
         self.assertEqual(ks.argv, sample_kernel_json['argv'])
         self.assertEqual(ks.display_name, sample_kernel_json['display_name'])
         self.assertEqual(ks.env, {})
     
     def test_install_kernel_spec(self):
         self.ksm.install_kernel_spec(self.installable_kernel,
                                      kernel_name='tstinstalled',
                                      user=True)
         self.assertIn('tstinstalled', self.ksm.find_kernel_specs())
         
         with self.assertRaises(OSError):
             self.ksm.install_kernel_spec(self.installable_kernel,
                                          kernel_name='tstinstalled',
                                          user=True)
         
         # Smoketest that this succeeds
         self.ksm.install_kernel_spec(self.installable_kernel,
                                      kernel_name='tstinstalled',
                                      replace=True, user=True)
 
-    @onlyif(kernelspec.find_install_prefix() in {'/usr', '/usr/local'}
-            and not os.access('/usr/local/share', os.W_OK),
-            "needs Unix system without root privileges")
+    @onlyif(os.name != 'nt' and not os.access('/usr/local/share', os.W_OK), "needs Unix system without root privileges")
     def test_cant_install_kernel_spec(self):
         with self.assertRaises(OSError):
             self.ksm.install_kernel_spec(self.installable_kernel,
                                          kernel_name='tstinstalled',
                                          user=False)