## Summary In `DiffDiscussionRow`, the `allResolved` computed property correctly supports auto-collapse when only one side of a parallel diff has resolvable discussions. This works because `.every()` on an empty array returns `true`, so the side with no discussions doesn't block the collapse. The existing unit tests don't exercise this path because the mock store returns the same discussions for both positions. ## Current behavior (correct) In a parallel diff where only one side has resolvable discussions: 1. User resolves all discussions on that side 2. `allResolved` iterates both positions via `this.positions.every()` 3. For the side with discussions, `.filter(d => !d.isForm && d.resolvable).every(d => d.resolved)` returns `true` (all resolved) 4. For the empty side, `findDiscussionsForPosition` returns `[]`, `.filter()` returns `[]`, and `.every()` returns `true` (no items to contradict the predicate) 5. `allResolved` becomes `true`, triggering auto-collapse This is correct - we don't want to force users to see discussions they can't resolve. ## Test gap The component test "auto-collapses one-sided discussions when all are resolved" in `diff_discussion_row_spec.js` uses a mock store whose `findDiscussionsForPosition()` always returns `this.discussions` regardless of the position argument. Both positions receive the same non-empty array of discussions, so the empty-array path is never exercised. The store-level test in `diff_discussions_spec.js` confirms `findDiscussionsForPosition` returns `[]` for non-matching positions, so the store half is covered. But the composition - where the component receives `[]` for one position and computes `allResolved` correctly - has no test. A future change like re-adding a `resolvable.length > 0` guard would silently break this behavior with no test failure. ## Suggested fix Either: - Add an integration-style test that uses the real `useDiffDiscussions` store with position-aware filtering and verifies auto-collapse for a one-sided parallel diff - Or make the mock store position-aware in the component test so that `findDiscussionsForPosition` returns discussions only for the matching position ## Related Introduced in https://gitlab.com/gitlab-org/gitlab/-/merge_requests/226730