gh-155648: Write the empty and placeholder IDLE tests

[serhiy-storchaka]

Several tests in idlelib/idle_test are empty stubs or placeholders that cannot fail. Write them instead of removing them.

• test_editor.RMenuTest was added in bpo-39885: IDLE: Leave selection when right click within #18951, which fixed right-clicking inside a selection, with the note that an automated test should follow. Its DummyRMenu class is used now to test right_menu_event(), together with the rmenu_check_*() methods that supply the menu entry states.
• test_configdialog.ConfigDialogTest was left with two empty stubs in bpo-30780: Add IDLE configdialog tests #3592, named after the two ConfigDialog methods which the button tests only check to be called. They are tested with a fake parent whose instance dictionary contains an autospecced EditorWindow.
• test_configdialog.ExtPageTest was added empty, with a commented out "Nothing here yet TODO" skip, when ExtPage was factored out in bpo-40468: Factor out class ExtPage in idlelib.configdialog #26618. The extensions page is the only configuration page without tests.
• test_grep.Default_commandTest was left empty in 2013 because GrepDialog.default_command() imports OutputWindow when called. The import cannot be moved to the top of the module due to an import loop, but the imported class can be replaced with a mock.
• test_config.ChangesTest.test_save_default never called save_all(), so it tested nothing. The test for the Save() calls asked for by the following TODO comment is added too.
• test_config.IdleConfTest.test_get_current_keyset only tested the non-darwin branch, because the default key sets no longer contain Alt keys. An extension binding with an Alt key is added, so that its replacement with Option can be tested.
• template.py lost the from idlelib import zzdummy line in gh-151428: Remove unused imports from stdlib #151478 as an unused import, but idle_test/README.txt instructs the user to replace zzdummy with the name of the module under test. A Ruff per-file ignore keeps it now.

Each new test was checked to fail when the corresponding code is broken.

The first two items are an alternative to the now merged #156257, which skipped these two stubs as empty. Its skips are removed here, because the tests are written. Its other changes, the vacuous assertion in test_autocomplete and the skipped dummy test in template.py, are left as they are.

• Issue: IDLE: Fix devdanzin test issues #155648

[terryjreedy]

I have not yet reviewed test_config dialog. Might put this off to review other PRs.
I partially reviewed test_editor, with one change so far and thinking about another.
Should be able to finish this tomorrow.
I reviewed the other five and requested 2 changes; approved with those changes.

[terryjreedy]

In this function, change parser to config in 2 for-loops.

[terryjreedy]

Please add the following comment under class RMenuTest... above.
# Test selection-rclick interaction in right_click_event and rmenu_check_copy(cut) status settings.
# These are part of the rmenu functions common to all text windows with context windows.

[terryjreedy]

Lets rewrite class as

class Dummy_grep:
    # Simplifications: 1. Don't initializes superclass SearchEngineBase with searchengine.
    # 2. Use directly set class vars instead of instance vars set from GUI.
    globvar = Var('')  # File name.
    recvar = Var(False)  # Recurse down directories?
    # Methods tested.
    grep_it = grep.GrepDialog.grep_it
    default_command = grep.GrepDialog.default_command  # Uses grep_it.

[bedevere-app]

When you're done making the requested changes, leave the comment: I have made the requested changes; please review again.

And if you don't make the requested changes, you will be poked with soft cushions!