bpo-5846: Do not use obsolete unittest functions. (GH-28303)

Get rid of use of makeSuite() and findTestCases().
Also make test_math and test_threading_local discoverable.

Lib/test/test_email/torture_test.py

@@ -12,7 +12,6 @@ import unittest
 from io import StringIO
 
 from test.test_email import TestEmailBase
-from test.support import run_unittest
 
 import email
 from email import __file__ as testfile
@@ -24,10 +23,11 @@ def openfile(filename):
     return open(path, 'r')
 
 # Prevent this test from running in the Python distro
-try:
-    openfile('crispin-torture.txt')
-except OSError:
-    raise unittest.SkipTest
+def setUpModule():
+    try:
+        openfile('crispin-torture.txt')
+    except OSError:
+        raise unittest.SkipTest
 
 
 
@@ -117,17 +117,11 @@ def _testclasses():
     return [getattr(mod, name) for name in dir(mod) if name.startswith('Test')]
 
 
-def suite():
-    suite = unittest.TestSuite()
+def load_tests(loader, tests, pattern):
+    suite = loader.suiteClass()
     for testclass in _testclasses():
-        suite.addTest(unittest.makeSuite(testclass))
+        suite.addTest(loader.loadTestsFromTestCase(testclass))
     return suite
 
-
-def test_main():
-    for testclass in _testclasses():
-        run_unittest(testclass)
-
-
-if __name__ == '__main__':
-    unittest.main(defaultTest='suite')
+if __name__ == "__main__":
+    unittest.main()