gh-105310: add decorator to skip rerunning tests

Lib/test/support/__init__.py

@@ -2457,3 +2457,34 @@ def adjust_int_max_str_digits(max_digits):
 
 #For recursion tests, easily exceeds default recursion limit
 EXCEEDS_RECURSION_LIMIT = 5000
+
+# A decorator to skip tests that are not rerunnable.
+def skip_rerun(reason):
+    """
+    This decorator skips the decorated test case
+    if it has already been run.
+    """
+    def decorator(test_case):
+
+        original_setUpClass = test_case.setUpClass
+        original_tearDownClass = test_case.tearDownClass
+
+        test_case._has_run = False
+
+        @classmethod
+        def setUpClass(cls):
+            if cls._has_run:
+                raise unittest.SkipTest(reason)
+            original_setUpClass()
+
+        @classmethod
+        def tearDownClass(cls):
+            original_tearDownClass()
+            cls._has_run = True
+
+        test_case.setUpClass = setUpClass
+        test_case.tearDownClass = tearDownClass
+
+        return test_case
+
+    return decorator

Lib/test/test_support.py

@@ -18,6 +18,7 @@
 from test.support import script_helper
 from test.support import socket_helper
 from test.support import warnings_helper
+from test.support import skip_rerun
 
 TESTFN = os_helper.TESTFN
 
@@ -684,6 +685,31 @@ def test_has_strftime_extensions(self):
         else:
             self.assertTrue(support.has_strftime_extensions)
 
+    def test_skip_rerun(self):
+        @skip_rerun("This test case does not support rerunning")
+        class TestCase(unittest.TestCase):
+            counter = 0
+
+            def test(self):
+                self.assertEqual(self.counter, 0)
+                self.__class__.counter += 1
+                self.assertEqual(self.counter, 1)
+
+        test_case = TestCase("test")
+
+        output = io.StringIO()
+        unittest.TextTestRunner(output).run(unittest.TestSuite([test_case]))
+        output.seek(0)
+        self.assertRegex(output.read(), "Ran 1 test")
+
+        output = io.StringIO()
+        unittest.TextTestRunner(output).run(unittest.TestSuite([test_case]))
+        output.seek(0)
+        self.assertRegex(output.read(), "Ran 0 tests")
+
+        self.assertEqual(TestCase.counter, 1)
+
+
     # XXX -follows a list of untested API
     # make_legacy_pyc
     # is_resource_enabled