Add unit test for Textualize#2900

tests/selection_list/test_over_wide_selections.py

@@ -0,0 +1,29 @@
+"""See https://github.com/Textualize/textual/issues/2900 for the reason behind these tests."""
+
+from textual.app import App, ComposeResult
+from textual.widgets import SelectionList
+
+
+class SelectionListApp(App[None]):
+    """Test selection list application."""
+
+    CSS = """
+    OptionList {
+        width: 20;
+    }
+    """
+
+    def compose(self) -> ComposeResult:
+        yield SelectionList[int](*[(f"{n} " * 10, n) for n in range(10)])
+
+
+async def test_over_wide_options() -> None:
+    """Options wider than the widget should not be an issue."""
+    async with SelectionListApp().run_test() as pilot:
+        assert pilot.app.query_one(SelectionList).highlighted == 0
+        await pilot.pause()
+        assert pilot.app.query_one(SelectionList).highlighted == 0
+
+
+if __name__ == "__main__":
+    SelectionListApp().run()