bpo-45229: Use doctest.DocTestSuite instead of run_doctest (GH-28468)

Alo use load_tests() for adding tests.

Lib/test/test_descrtut.py

@@ -10,6 +10,9 @@
 
 from test.support import sortdict
 import pprint
+import doctest
+import unittest
+
 
 class defaultdict(dict):
     def __init__(self, default=None):
@@ -469,19 +472,10 @@ __test__ = {"tut1": test_1,
             "tut7": test_7,
             "tut8": test_8}
 
-# Magic test name that regrtest.py invokes *after* importing this module.
-# This worms around a bootstrap problem.
-# Note that doctest and regrtest both look in sys.argv for a "-v" argument,
-# so this works as expected in both ways of running regrtest.
-def test_main(verbose=None):
-    # Obscure:  import this module as test.test_descrtut instead of as
-    # plain test_descrtut because the name of this module works its way
-    # into the doctest examples, and unless the full test.test_descrtut
-    # business is used the name can change depending on how the test is
-    # invoked.
-    from test import support, test_descrtut
-    support.run_doctest(test_descrtut, verbose)
+def load_tests(loader, tests, pattern):
+    tests.addTest(doctest.DocTestSuite())
+    return tests
+
 
-# This part isn't needed for regrtest, but for running the test directly.
 if __name__ == "__main__":
-    test_main(1)
+    unittest.main()