Extend ListView test to test an empty inherited list

For testing permutations of Textualize#1588.

tests/listview/test_inherit_listview.py

@@ -3,23 +3,42 @@
 
 
 class MyListView(ListView):
+    """Test child class of a ListView."""
+
+    def __init__(self, items: int = 0) -> None:
+        super().__init__()
+        self._items = items
+
     def compose(self) -> ComposeResult:
         """Compose the child widgets."""
-        for n in range(20):
-            yield ListView(Label(f"This is item {n}"))
+        for n in range(self._items):
+            yield ListItem(Label(f"This is item {n}"))
 
 
 class ListViewApp(App[None]):
     """ListView test app."""
 
+    def __init__(self, items: int = 0) -> None:
+        super().__init__()
+        self._items = items
+
     def compose(self) -> ComposeResult:
         """Compose the child widgets."""
-        yield MyListView()
+        yield MyListView(self._items)
 
 
-async def test_inherited_list_view() -> None:
-    """A self-populating inherited ListView should work as normal."""
+async def test_empty_inherited_list_view() -> None:
+    """An empty self-populating inherited ListView should work as expected."""
     async with ListViewApp().run_test() as pilot:
+        await pilot.press("tab")
+        assert pilot.app.query_one(MyListView).index is None
+        await pilot.press("down")
+        assert pilot.app.query_one(MyListView).index is None
+
+
+async def test_populated_inherited_list_view() -> None:
+    """A self-populating inherited ListView should work as normal."""
+    async with ListViewApp(30).run_test() as pilot:
         await pilot.press("tab")
         assert pilot.app.query_one(MyListView).index == 0
         await pilot.press("down")