Factor out common boilerplate for test_support
diff --git a/Lib/test/test_support.py b/Lib/test/test_support.py
index c61e194..56b60cc 100644
--- a/Lib/test/test_support.py
+++ b/Lib/test/test_support.py
@@ -233,6 +233,12 @@
     """Run tests from a unittest.TestCase-derived class."""
     run_suite(unittest.makeSuite(testclass), testclass)
 
+def run_classtests(*classnames):
+    suite = unittest.TestSuite()
+    for cls in classnames:
+        suite.addTest(unittest.makeSuite(cls))
+    run_suite(suite)
+
 
 #=======================================================================
 # doctest driver.