Show and Destroy the test dialogs on Macs, yield after update, and more test fixes

(cherry picked from commit 7f2e86a72c)

unittests/test_dialog.py

@@ -20,6 +20,10 @@ class dialog_Tests(wtc.WidgetTestCase):
             dlg.Destroy()
             self.assertTrue(val == wx.ID_OK)
             self.myYield()
+        else:
+            dlg.Show()
+            dlg.Destroy()
+            self.myYield()
 
 
     def test_dialogDefaultCtor(self):

unittests/test_sizer.py

@@ -74,12 +74,14 @@ class sizer_Tests(wtc.WidgetTestCase):
     def test_iter(self):
         bs = wx.BoxSizer()
         widgetlist = [wx.Panel(self.frame) for _ in range(5)]
+        for w in widgetlist:
+            bs.Add(w)
 
         sizeritems = [x for x in bs]
         for item in sizeritems:
             self.assertTrue(isinstance(item, wx.SizerItem))
 
-        self.assertTrue([x.GetWidget() for x in bs] == widgetlist)
+        self.assertEqual([x.GetWindow() for x in bs], widgetlist)
 
     def test_sizerSpacers1(self):
         bs = wx.BoxSizer()

unittests/wtc.py

@@ -57,6 +57,7 @@ class WidgetTestCase(unittest.TestCase):
         if 'wxOSX' in wx.PlatformInfo:
             wx.MilliSleep(40)  # a little more than 1/30, just in case
         window.Update()
+        self.myYield()
 
 
     def closeDialogs(self):