@Test
    public void testStoreNullSessionId() {
        assertThrows(IllegalArgumentException.class, () -> keyManager.storeSessionKey(null, testKey, "AES"));
    }

    @Test
    public void testUseAfterClose() {
        keyManager.close();
        assertThrows(IllegalStateException.class, () -> keyManager.storeSessionKey("session", testKey, "AES"));
    }

    @Test
    public void testMultipleCloseCalls() {