test: carousel core change/destroy edge cases

tests/core.test.ts

@@ -55,3 +55,33 @@ test('next/prev clamp to range and scroll to target offset', () => {
   c.next();
   expect(track.scrollTo).toHaveBeenCalled();
 });
+
+test('change fires with new index when a slide intersects', () => {
+  const c = createCarousel(track);
+  const seen: number[] = [];
+  c.on('change', (i) => seen.push(i));
+  (IOShim.last as IOShim).emit(2); // user swiped to slide 2
+  expect(seen).toEqual([2]);
+  expect(c.index).toBe(2);
+});
+
+test('change does not re-fire for the same index', () => {
+  const c = createCarousel(track);
+  const seen: number[] = [];
+  c.on('change', (i) => seen.push(i));
+  (IOShim.last as IOShim).emit(1);
+  (IOShim.last as IOShim).emit(1);
+  expect(seen).toEqual([1]);
+});
+
+test('unsubscribe stops delivery; destroy disconnects observer', () => {
+  const c = createCarousel(track);
+  const seen: number[] = [];
+  const off = c.on('change', (i) => seen.push(i));
+  off();
+  (IOShim.last as IOShim).emit(2);
+  expect(seen).toEqual([]);
+  const spy = vi.spyOn(IOShim.last as IOShim, 'disconnect');
+  c.destroy();
+  expect(spy).toHaveBeenCalled();
+});