test: harden business boundary conditions

apps/server/src/classes/classes.scope.spec.ts

@@ -41,7 +41,10 @@ describe('ClassesService — teacher data scope', () => {
 it('clears denormalized teacher ids when the last teacher for that role is removed', async () => {
   const classRepo = { update: jest.fn() };
   const classTeacherRepo = {
-    find: jest.fn().mockResolvedValue([]),
+    find: jest
+      .fn()
+      .mockResolvedValueOnce([{ id: 1, classId: 8, userId: 21 }])
+      .mockResolvedValueOnce([]),
     delete: jest.fn().mockResolvedValue({ affected: 1 }),
   };
   const service = new ClassesService(