Integration: #2086 test that the strip beside the column headings is filled in dark mode

crates/ui-egui/tests/scrollbar_column_fill.rs

@@ -0,0 +1,28 @@
+//! The strip beside the column headings, above the vertical scrollbar, takes the bar colour in
+//! dark mode instead of showing a light square (#2086).
+
+use egui::{Shape, pos2};
+use gridcraft_engine::Session;
+use gridcraft_ui_egui::{SheetApp, theme::Tokens};
+use serde_json::json;
+
+#[test]
+fn dark_theme_fills_the_strip_right_of_the_last_column_heading() {
+    let mut session = Session::new();
+    session.new_workbook();
+    let mut h = egui_kittest::Harness::builder().with_size(egui::vec2(1200.0, 800.0)).build_ui_state(
+        |ui, app: &mut SheetApp| {
+            app.logic(ui.ctx());
+            app.ui(ui);
+        },
+        SheetApp::new(session, Default::default()),
+    );
+    h.state_mut().run("view.theme", json!({"mode": "dark"})).unwrap();
+    h.run_steps(6);
+    let grid = h.state().grid.rect.expect("grid rect");
+    // Inside the scrollbar column, at the height of the column headings.
+    let probe = pos2(grid.right() + 7.0, grid.top() + 5.0);
+    let fill = Tokens::dark().tab_bar;
+    let covered = h.output().shapes.iter().any(|s| matches!(&s.shape, Shape::Rect(r) if r.fill == fill && r.rect.contains(probe)));
+    assert!(covered, "no tab_bar fill covers {probe:?}");
+}