assertEquals(ChatMessage.ROLE_USER, messages.get(0).getRole());
        assertEquals("User 3", messages.get(0).getContent());
    }

    @Test
    public void test_trimHistoryEvenPairs() {
        final ChatSession session = new ChatSession();
        // 8 messages: 4 user/assistant pairs
        for (int i = 1; i <= 4; i++) {
            session.addUserMessage("User " + i);