Add DataTable medium-sized test for clearing

tests/test_data_table.py

@@ -0,0 +1,36 @@
+from textual.app import App
+from textual.coordinate import Coordinate
+from textual.widgets import DataTable
+
+
+class DataTableApp(App):
+    def compose(self):
+        yield DataTable()
+
+
+async def test_clear():
+    app = DataTableApp()
+    async with app.run_test():
+        table = app.query_one(DataTable)
+        assert table.cursor_cell == Coordinate(0, 0)
+        assert table.hover_cell == Coordinate(0, 0)
+
+        # Add some data and update cursor positions
+        table.add_column("Column0")
+        table.add_rows([["Row0"], ["Row1"], ["Row2"]])
+        table.cursor_cell = Coordinate(1, 0)
+        table.hover_cell = Coordinate(2, 0)
+
+        # Ensure the cursor positions are reset to origin on clear()
+        table.clear()
+        assert table.cursor_cell == Coordinate(0, 0)
+        assert table.hover_cell == Coordinate(0, 0)
+
+        # Ensure that the table has been cleared
+        assert table.data == {}
+        assert table.rows == {}
+        assert len(table.columns) == 1
+
+        # Clearing the columns too
+        table.clear(columns=True)
+        assert len(table.columns) == 0