bpo-33906: Rename idlelib.windows as window (#7833)

Match Window on the main menu and remove last plural module name.
Change imports, test, and attribute references to match new name.

Lib/idlelib/idle_test/test_window.py

@@ -0,0 +1,45 @@
+"Test window, coverage 47%."
+
+from idlelib import window
+import unittest
+from test.support import requires
+from tkinter import Tk
+
+
+class WindowListTest(unittest.TestCase):
+
+    def test_init(self):
+        wl = window.WindowList()
+        self.assertEqual(wl.dict, {})
+        self.assertEqual(wl.callbacks, [])
+
+    # Further tests need mock Window.
+
+
+class ListedToplevelTest(unittest.TestCase):
+
+    @classmethod
+    def setUpClass(cls):
+        window.registry = set()
+        requires('gui')
+        cls.root = Tk()
+        cls.root.withdraw()
+
+    @classmethod
+    def tearDownClass(cls):
+        window.registry = window.WindowList()
+        cls.root.update_idletasks()
+##        for id in cls.root.tk.call('after', 'info'):
+##            cls.root.after_cancel(id)  # Need for EditorWindow.
+        cls.root.destroy()
+        del cls.root
+
+    def test_init(self):
+
+        win = window.ListedToplevel(self.root)
+        self.assertIn(win, window.registry)
+        self.assertEqual(win.focused_widget, win)
+
+
+if __name__ == '__main__':
+    unittest.main(verbosity=2)