Add tests for the positional children argument for selection containers.

Author: jasongrout

python/ipywidgets/ipywidgets/widgets/tests/test_selectioncontainer.py

@@ -5,7 +5,7 @@
 
 from traitlets import TraitError
 
-from ipywidgets.widgets import Accordion, HTML
+from ipywidgets.widgets import Accordion, Tab, Stack, HTML
 
 
 class TestAccordion(TestCase):
@@ -27,6 +27,11 @@ def test_selected_index_out_of_bounds(self):
         with self.assertRaises(TraitError):
             Accordion(self.children, selected_index=-1)
 
+    def test_children_position_argument(self):
+        Accordion(self.children)
+        Tab(self.children)
+        Stack(self.children)
+
 
     def test_titles(self):
         accordion = Accordion(self.children, selected_index=None)