Tests: the Paintbrush closing cursor follows the point a release keeps

The Paintbrush drops a sample less than a pixel from the last kept
point, and a release there keeps that point. The new test moves the
pointer inside Close Paths When Ends Are Within while the kept point
stays outside it, and checks that the cursor shows no closing ring and
that the release leaves the path open.

crates/tools/src/draw2/gesture.rs

@@ -1282,6 +1282,31 @@ mod tests {
         }
     }
 
+    /// A Paintbrush sample under a pixel from the last point is dropped, and a release there keeps
+    /// the last point: the closing cursor follows that point, not the pointer.
+    #[test]
+    fn the_paintbrush_closing_cursor_follows_the_point_a_release_keeps() {
+        let (d, _) = doc_with_rect();
+        let s = Selection::default();
+        let p = paint();
+        let cx = cx(&d, &s, &p);
+        let none = Mods::default();
+        let mut t = GestureTool::new("paintbrush");
+        t.set_option("closeWithin", &json!(15.0));
+        for (k, x, y) in [(PointerKind::Down, 310.0, 330.0), (PointerKind::Drag, 360.0, 350.0), (PointerKind::Drag, 330.0, 390.0)] {
+            t.pointer(&cx, &PointerEvent::new(k, x, y));
+        }
+        // The last point kept is 15.5 from the start, outside Close Paths When Ends Are Within.
+        t.pointer(&cx, &PointerEvent::new(PointerKind::Drag, 325.5, 330.0));
+        assert_eq!(t.cursor(&cx, Point::new(325.5, 330.0), none), Cursor::Paintbrush, "outside the closing distance");
+        // The pointer moves 0.7 to 14.8 from the start; the sample is dropped.
+        t.pointer(&cx, &PointerEvent::new(PointerKind::Drag, 324.8, 330.0));
+        assert_eq!(t.cursor(&cx, Point::new(324.8, 330.0), none), Cursor::Paintbrush, "the dropped sample shows no ring");
+        let acts = t.pointer(&cx, &PointerEvent::new(PointerKind::Up, 324.8, 330.0));
+        let Some(Action::Preview(_, v)) = acts.first() else { panic!("{acts:?}") };
+        assert_eq!(v["closed"], json!(false), "the release keeps the last point and leaves the path open");
+    }
+
     #[test]
     fn eraser_and_knife_exec_on_release() {
         let (d, _) = doc_with_rect();