Advertise “python -m” instead of direct filename.

Doc/library/test.rst

@@ -168,14 +168,14 @@ whether the test passed or failed and thus minimize output.
 
 Running :mod:`test.regrtest` directly allows what resources are available for
 tests to use to be set. You do this by using the ``-u`` command-line
-option. Run :program:`python regrtest.py -uall` to turn on all
+option. Run :program:`python -m regrtest -uall` to turn on all
 resources; specifying ``all`` as an option for ``-u`` enables all
 possible resources. If all but one resource is desired (a more common case), a
 comma-separated list of resources that are not desired may be listed after
-``all``. The command :program:`python regrtest.py -uall,-audio,-largefile`
+``all``. The command :program:`python -m regrtest -uall,-audio,-largefile`
 will run :mod:`test.regrtest` with all resources except the ``audio`` and
 ``largefile`` resources. For a list of all resources and more command-line
-options, run :program:`python regrtest.py -h`.
+options, run :program:`python -m regrtest -h`.
 
 Some other ways to execute the regression tests depend on what platform the
 tests are being executed on. On Unix, you can run :program:`make test` at the