chain.delete(null);

        assertEquals(1, chain.deleteCalls.size());
        assertNull(chain.deleteCalls.get(0));
    }

    // Test delete with multiple users
    public void test_delete_multipleUsers() {
        TestAuthenticationChain chain = new TestAuthenticationChain();
        List<User> users = new ArrayList<>();
        for (int i = 0; i < 5; i++) {