diff -r 4b42d7f288c5 Lib/test/test_genericpath.py
--- a/Lib/test/test_genericpath.py	Thu Jan 03 09:22:41 2013 +0100
+++ b/Lib/test/test_genericpath.py	Thu Jan 03 09:00:55 2013 -0600
@@ -17,9 +17,7 @@
         pass
 
 
-class GenericTest(unittest.TestCase):
-    # The path module to be tested
-    pathmodule = genericpath
+class GenericTest:
     common_attributes = ['commonprefix', 'getsize', 'getatime', 'getctime',
                          'getmtime', 'exists', 'isdir', 'isfile']
     attributes = []
@@ -270,13 +268,16 @@
             self.assertTrue(self.pathmodule.sameopenfile(
                                 a.fileno(), b.fileno()))
 
+class TestGenericTest(GenericTest, unittest.TestCase):
+    # Issue 16748: GenericTest can't inherit from unittest.TestCase
+    # for test discovery purposes; CommonTest inherits from GenericTest
+    # and is only meant to be inherited by others.
+    pathmodule = genericpath
 
 # Following TestCase is not supposed to be run from test_genericpath.
 # It is inherited by other test modules (macpath, ntpath, posixpath).
 
 class CommonTest(GenericTest):
-    # The path module to be tested
-    pathmodule = None
     common_attributes = GenericTest.common_attributes + [
         # Properties
         'curdir', 'pardir', 'extsep', 'sep',
@@ -408,7 +409,7 @@
 
 
 def test_main():
-    support.run_unittest(GenericTest)
+    support.run_unittest(TestGenericTest)
 
 
 if __name__=="__main__":
diff -r 4b42d7f288c5 Lib/test/test_macpath.py
--- a/Lib/test/test_macpath.py	Thu Jan 03 09:22:41 2013 +0100
+++ b/Lib/test/test_macpath.py	Thu Jan 03 09:00:55 2013 -0600
@@ -115,7 +115,7 @@
         self.assertEqual(normpath(b"a:b:"), b"a:b")
 
 
-class MacCommonTest(test_genericpath.CommonTest):
+class MacCommonTest(test_genericpath.CommonTest, unittest.TestCase):
     pathmodule = macpath
 
 
diff -r 4b42d7f288c5 Lib/test/test_ntpath.py
--- a/Lib/test/test_ntpath.py	Thu Jan 03 09:22:41 2013 +0100
+++ b/Lib/test/test_ntpath.py	Thu Jan 03 09:00:55 2013 -0600
@@ -257,7 +257,7 @@
                     ntpath.sameopenfile(-1, -1)
 
 
-class NtCommonTest(test_genericpath.CommonTest):
+class NtCommonTest(test_genericpath.CommonTest, unittest.TestCase):
     pathmodule = ntpath
     attributes = ['relpath', 'splitunc']
 
diff -r 4b42d7f288c5 Lib/test/test_posixpath.py
--- a/Lib/test/test_posixpath.py	Thu Jan 03 09:22:41 2013 +0100
+++ b/Lib/test/test_posixpath.py	Thu Jan 03 09:00:55 2013 -0600
@@ -462,7 +462,7 @@
             os.getcwdb = real_getcwdb
 
 
-class PosixCommonTest(test_genericpath.CommonTest):
+class PosixCommonTest(test_genericpath.CommonTest, unittest.TestCase):
     pathmodule = posixpath
     attributes = ['relpath', 'samefile', 'sameopenfile', 'samestat']