diff --git a/frontend/src/lib/components/AnnotationLayer.svelte.test.ts b/frontend/src/lib/components/AnnotationLayer.svelte.test.ts
index 81b87a84..1f549cd3 100644
--- a/frontend/src/lib/components/AnnotationLayer.svelte.test.ts
+++ b/frontend/src/lib/components/AnnotationLayer.svelte.test.ts
@@ -64,4 +64,32 @@ describe('AnnotationLayer', () => {
 			expect(clickedId).toBe('ann-1');
 		});
 	});
+
+	describe('flashAnnotationId prop', () => {
+		it('should apply annotation-flash class when flashAnnotationId matches', async () => {
+			render(AnnotationLayer, {
+				annotations: [annotation],
+				canDraw: false,
+				color: '#00c7b1',
+				flashAnnotationId: 'ann-1',
+				onDraw: () => {}
+			});
+
+			const el = document.querySelector('[data-testid="annotation-ann-1"]')!;
+			expect(el.classList.contains('annotation-flash')).toBe(true);
+		});
+
+		it('should not apply annotation-flash class when flashAnnotationId does not match', async () => {
+			render(AnnotationLayer, {
+				annotations: [annotation],
+				canDraw: false,
+				color: '#00c7b1',
+				flashAnnotationId: 'other-id',
+				onDraw: () => {}
+			});
+
+			const el = document.querySelector('[data-testid="annotation-ann-1"]')!;
+			expect(el.classList.contains('annotation-flash')).toBe(false);
+		});
+	});
 });