#14533: if a test has no test_main, use loadTestsFromModule.

This moves us further in the direction of using normal unittest facilities
instead of specialized regrtest ones.  Any test module that can be correctly
run currently using 'python unittest -m test.test_xxx' can now be converted to
use normal unittest test loading by simply deleting its test_main, thus no
longer requiring manual maintenance of the list of tests to run.  (Not all
tests can be converted that easily, since test_main sometimes does some
additional things (such as reap_children or reap_threads).  In those cases the
extra code may be moved to setUpModule/tearDownModule methods, or perhaps the
same ends can be achieved in a different way, such as moving the decorators to
the test classes that need them, etc.)

I don't advocate going through and making this change wholesale, but any time
a list of tests in test_main would otherwise need to be updated, consideration
should instead be given to deleting test_main.

Lib/test/regrtest.py

@@ -1228,14 +1228,15 @@ def runtest_inner(test, verbose, quiet,
             start_time = time.time()
             the_package = __import__(abstest, globals(), locals(), [])
             the_module = getattr(the_package, test)
-            # Old tests run to completion simply as a side-effect of
-            # being imported.  For tests based on unittest or doctest,
-            # explicitly invoke their test_main() function (if it exists).
-            indirect_test = getattr(the_module, "test_main", None)
-            if indirect_test is not None:
-                indirect_test()
+            # If the test has a test_main, that will run the appropriate
+            # tests.  If not, use normal unittest test loading.
+            test_runner = getattr(the_module, "test_main", None)
+            if test_runner is None:
+                tests = unittest.TestLoader().loadTestsFromModule(the_module)
+                test_runner = lambda: support.run_unittest(tests)
+            test_runner()
             if huntrleaks:
-                refleak = dash_R(the_module, test, indirect_test,
+                refleak = dash_R(the_module, test, test_runner,
                     huntrleaks)
             test_time = time.time() - start_time
     except support.ResourceDenied as msg: