Add a test and remove dead code (#3514)

* Remove dead code.

MouseScrollUp and MouseScrollDown inherit from MouseEvent so this branch is never taken.

* Add screen test.

src/textual/screen.py

@@ -976,17 +976,6 @@ def _forward_event(self, event: events.Event) -> None:
                 else:
                     widget._forward_event(event._apply_offset(-region.x, -region.y))
 
-        elif isinstance(event, (events.MouseScrollDown, events.MouseScrollUp)):
-            try:
-                widget, _region = self.get_widget_at(event.x, event.y)
-            except errors.NoWidget:
-                return
-            scroll_widget = widget
-            if scroll_widget is not None:
-                if scroll_widget is self:
-                    self.post_message(event)
-                else:
-                    scroll_widget._forward_event(event)
         else:
             self.post_message(event)
 

tests/test_screens.py

@@ -6,10 +6,10 @@
 
 from textual import work
 from textual.app import App, ComposeResult, ScreenStackError
-from textual.events import MouseMove
+from textual.events import MouseMove, MouseScrollDown, MouseScrollUp
 from textual.geometry import Offset
 from textual.screen import Screen
-from textual.widgets import Button, Input, Label
+from textual.widgets import Button, DataTable, Input, Label
 from textual.worker import NoActiveWorker
 
 skip_py310 = pytest.mark.skipif(
@@ -304,6 +304,25 @@ async def key_p(self) -> None:
             app.bottom.dismiss()
 
 
+async def test_dismiss_action():
+    class ConfirmScreen(Screen[bool]):
+        BINDINGS = [("y", "dismiss(True)", "Dismiss")]
+
+    class MyApp(App[None]):
+        bingo = False
+
+        def on_mount(self) -> None:
+            self.push_screen(ConfirmScreen(), callback=self.callback)
+
+        def callback(self, result: bool) -> None:
+            self.bingo = result
+
+    app = MyApp()
+    async with app.run_test() as pilot:
+        await pilot.press("y")
+        assert app.bingo
+
+
 async def test_switch_screen_no_op():
     """Regression test for https://github.com/Textualize/textual/issues/2650"""