bpo-39388: IDLE: Fix bug when cancelling out of configdialog (GH-18068)

Co-authored-by: Terry Jan Reedy <tjreedy@udel.edu>

Lib/idlelib/NEWS.txt

@@ -3,7 +3,9 @@ Released on 2020-10-05?
 ======================================
 
 
-bpo-39050: Make Settings dialog Help button work again.
+bpo-39388: Settings dialog Cancel button cancels pending changes.
+
+bpo-39050: Settings dialog Help button again displays help text.
 
 bpo-32989: Add tests for editor newline_and_indent_event method.
 Remove unneeded arguments and dead code from pyparse

Lib/idlelib/configdialog.py

@@ -191,6 +191,7 @@ class ConfigDialog(Toplevel):
         Methods:
             destroy: inherited
         """
+        changes.clear()
         self.destroy()
 
     def destroy(self):

Lib/idlelib/idle_test/test_configdialog.py

@@ -47,17 +47,24 @@ def tearDownModule():
     root.destroy()
     root = dialog = None
 
-class ConfigDialogTest(unittest.TestCase):
 
-    def test_help(self):
+class DialogTest(unittest.TestCase):
+
+    @mock.patch(__name__+'.dialog.destroy', new_callable=Func)
+    def test_cancel(self, destroy):
+        changes['main']['something'] = 1
+        dialog.cancel()
+        self.assertEqual(changes['main'], {})
+        self.assertEqual(destroy.called, 1)
+
+    @mock.patch('idlelib.configdialog.view_text', new_callable=Func)
+    def test_help(self, view):
         dialog.note.select(dialog.keyspage)
-        saved = configdialog.view_text
-        view = configdialog.view_text = Func()
         dialog.help()
         s = view.kwds['contents']
-        self.assertTrue(s.startswith('When you click'))
+        self.assertTrue(s.startswith('When you click') and
-        self.assertTrue(s.endswith('a different name.\n'))
+                        s.endswith('a different name.\n'))
-        configdialog.view_text = saved
+
 
 class FontPageTest(unittest.TestCase):
     """Test that font widgets enable users to make font changes.

Misc/NEWS.d/next/IDLE/2020-01-25-02-26-45.bpo-39388.x4TQNh.rst

@@ -0,0 +1 @@
+IDLE Settings Cancel button now cancels pending changes