ElyMark: outside changes tested through the window; a reload keeps its place (C14.11)

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

apps/ely-mark/src/compare.rs

@@ -190,3 +190,36 @@ enum Choice {
     Mine,
     Merged,
 }
+
+#[cfg(test)]
+mod tests {
+    use gpui::TestAppContext;
+
+    use super::Choice;
+    use crate::outside::tests::{look, opened, shown};
+
+    #[gpui::test]
+    fn a_merge_lands_as_one_undo_step(cx: &mut TestAppContext) {
+        let (desk, cx, id, path, _dirs) = opened("a\n\nb\n", cx);
+        let view = desk.read_with(cx, |desk, _| desk.active_view().expect("a tab"));
+        view.update(cx, |view, cx| view.adopt("a\n\nb\n\nmine\n".into(), cx));
+        cx.run_until_parked();
+        std::fs::write(&path, "theirs\n\na\n\nb\n").expect("an outside write");
+        look(&desk, id, cx);
+        desk.update(cx, |desk, cx| desk.compare(id, cx));
+        desk.update_in(cx, |desk, window, cx| {
+            desk.settle(Choice::Merged, window, cx)
+        });
+        cx.run_until_parked();
+        assert_eq!(shown(&desk, cx), "theirs\n\na\n\nb\n\nmine\n");
+        let focus = view.read_with(cx, |view, _| view.focus.clone());
+        cx.update(|window, cx| window.focus(&focus, cx));
+        cx.run_until_parked();
+        cx.simulate_keystrokes("secondary-z");
+        assert_eq!(
+            shown(&desk, cx),
+            "a\n\nb\n\nmine\n",
+            "one undo takes the merge back"
+        );
+    }
+}