Issue #14664: It is now possible to use @unittest.skip{If,Unless} on a test class that doesn't inherit from TestCase (i.e. a mixin).

Lib/unittest/case.py

@@ -62,7 +62,7 @@ def skip(reason):
     Unconditionally skip a test.
     """
     def decorator(test_item):
-        if not (isinstance(test_item, type) and issubclass(test_item, TestCase)):
+        if not isinstance(test_item, type):
             @functools.wraps(test_item)
             def skip_wrapper(*args, **kwargs):
                 raise SkipTest(reason)

Lib/unittest/test/test_skipping.py

@@ -66,6 +66,21 @@ class Test_TestSkipping(unittest.TestCase):
         self.assertEqual(result.skipped, [(test, "testing")])
         self.assertEqual(record, [])
 
+    def test_skip_non_unittest_class(self):
+        @unittest.skip("testing")
+        class Mixin:
+            def test_1(self):
+                record.append(1)
+        class Foo(Mixin, unittest.TestCase):
+            pass
+        record = []
+        result = unittest.TestResult()
+        test = Foo("test_1")
+        suite = unittest.TestSuite([test])
+        suite.run(result)
+        self.assertEqual(result.skipped, [(test, "testing")])
+        self.assertEqual(record, [])
+
     def test_expected_failure(self):
         class Foo(unittest.TestCase):
             @unittest.expectedFailure

Misc/NEWS

@@ -56,6 +56,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #14664: It is now possible to use @unittest.skip{If,Unless} on a
+  test class that doesn't inherit from TestCase (i.e. a mixin).
+
 - Issue #14160: TarFile.extractfile() failed to resolve symbolic links when
   the links were not located in an archive subdirectory.