Refactor code structure for improved readability and maintainability

apps/backend/test/complex/invite-complex-user.test.ts

@@ -80,7 +80,7 @@ test('rejects when the invite target already belongs to the complex', async () =
   }
 
   expect(caught).toBeInstanceOf(ComplexMembersError);
-  expect((caught as ComplexMembersError).status).toBe(409);
+  expect((caught as InstanceType<typeof ComplexMembersError>).status).toBe(409);
   expect(transactionMock).not.toHaveBeenCalled();
   expect(sendMailMock).not.toHaveBeenCalled();
 });