test

src/textual/app.py

@@ -418,7 +418,10 @@ class App(Generic[ReturnType], DOMNode):
 
     @property
     def screen(self) -> Screen:
-        return self._screen_stack[-1]
+        try:
+            return self._screen_stack[-1]
+        except IndexError:
+            raise ScreenStackError("No screens on stack") from None
 
     @property
     def size(self) -> Size:

tests/test_screens.py

@@ -10,6 +10,9 @@ async def test_screens():
     app = App()
     app._set_active()
 
+    with pytest.raises(ScreenStackError):
+        app.screen
+
     assert not app._installed_screens
 
     screen1 = Screen(name="screen1")