diff --git a/tests/llm/test_discussion.py b/tests/llm/test_discussion.py
new file mode 100644
index 000000000..ecebd8d9e
--- /dev/null
+++ b/tests/llm/test_discussion.py
@@ -0,0 +1,293 @@
+"""Unit tests for the Discussion class and related HTML tag parsing utilities in llm_utils."""
+
+import pytest
+
+from agentlab.llm.llm_utils import (
+    AIMessage,
+    BaseMessage,
+    Discussion,
+    HumanMessage,
+    ParseError,
+    SystemMessage,
+    extract_html_tags,
+    parse_html_tags,
+    parse_html_tags_raise,
+)
+
+
+# ---------------------------------------------------------------------------
+# Discussion – construction
+# ---------------------------------------------------------------------------
+
+
+class TestDiscussionInit:
+    def test_empty_init(self):
+        d = Discussion()
+        assert len(d) == 0
+        assert list(d) == []
+
+    def test_init_with_single_message(self):
+        msg = SystemMessage("Hello")
+        d = Discussion(msg)
+        assert len(d) == 1
+        assert d[0]["content"] == "Hello"
+
+    def test_init_with_list_of_messages(self):
+        msgs = [SystemMessage("A"), HumanMessage("B"), AIMessage("C")]
+        d = Discussion(msgs)
+        assert len(d) == 3
+        assert d[0]["role"] == "system"
+        assert d[1]["role"] == "user"
+        assert d[2]["role"] == "assistant"
+
+
+# ---------------------------------------------------------------------------
+# Discussion – add_message / append
+# ---------------------------------------------------------------------------
+
+
+class TestDiscussionAddMessage:
+    def test_add_message_from_base_message(self):
+        d = Discussion()
+        d.add_message(SystemMessage("sys"))
+        assert len(d) == 1
+        assert d[0]["role"] == "system"
+
+    def test_add_message_from_dict(self):
+        d = Discussion()
+        d.add_message({"role": "user", "content": "hi"})
+        assert len(d) == 1
+        assert d[0]["content"] == "hi"
+
+    def test_add_message_from_role_content(self):
+        d = Discussion()
+        d.add_message(role="assistant", content="reply")
+        assert len(d) == 1
+        assert d[0]["role"] == "assistant"
+        assert d[0]["content"] == "reply"
+
+    def test_append_delegates_to_add_message(self):
+        d = Discussion()
+        d.append(HumanMessage("test"))
+        assert len(d) == 1
+        assert d[0]["content"] == "test"
+
+
+# ---------------------------------------------------------------------------
+# Discussion – properties & dunder methods
+# ---------------------------------------------------------------------------
+
+
+class TestDiscussionProperties:
+    def test_last_message(self):
+        d = Discussion([SystemMessage("first"), HumanMessage("second")])
+        assert d.last_message["content"] == "second"
+
+    def test_len(self):
+        d = Discussion([SystemMessage("a"), HumanMessage("b")])
+        assert len(d) == 2
+
+    def test_getitem(self):
+        d = Discussion([SystemMessage("a"), HumanMessage("b")])
+        assert d[0]["content"] == "a"
+        assert d[1]["content"] == "b"
+
+    def test_iter(self):
+        msgs = [SystemMessage("a"), HumanMessage("b")]
+        d = Discussion(msgs)
+        contents = [m["content"] for m in d]
+        assert contents == ["a", "b"]
+
+    def test_str(self):
+        d = Discussion([SystemMessage("hello"), HumanMessage("world")])
+        s = str(d)
+        assert "hello" in s
+        assert "world" in s
+
+
+# ---------------------------------------------------------------------------
+# Discussion – merge / to_string / to_openai / to_markdown
+# ---------------------------------------------------------------------------
+
+
+class TestDiscussionConversions:
+    def test_to_string_merges(self):
+        msg = BaseMessage(
+            role="user",
+            content=[
+                {"type": "text", "text": "part1"},
+                {"type": "text", "text": "part2"},
+            ],
+        )
+        d = Discussion([msg])
+        result = d.to_string()
+        assert "part1" in result
+        assert "part2" in result
+
+    def test_to_openai_returns_messages(self):
+        d = Discussion([SystemMessage("sys"), HumanMessage("usr")])
+        msgs = d.to_openai()
+        assert len(msgs) == 2
+        assert msgs[0]["role"] == "system"
+
+    def test_to_markdown(self):
+        d = Discussion([SystemMessage("hello")])
+        md = d.to_markdown()
+        assert "Message 0" in md
+        assert "hello" in md
+
+
+# ---------------------------------------------------------------------------
+# Discussion – add_text / add_content on last message
+# ---------------------------------------------------------------------------
+
+
+class TestDiscussionContentHelpers:
+    def test_add_text_to_last_message(self):
+        d = Discussion([HumanMessage("first")])
+        d.add_text("extra")
+        # After add_text the content should be a list with two text entries
+        assert isinstance(d.last_message["content"], list)
+        texts = [
+            e["text"] for e in d.last_message["content"] if e["type"] == "text"
+        ]
+        assert "first" in texts
+        assert "extra" in texts
+
+    def test_add_content_to_last_message(self):
+        d = Discussion([HumanMessage("msg")])
+        d.add_content("text", "added")
+        assert isinstance(d.last_message["content"], list)
+        assert len(d.last_message["content"]) == 2
+
+
+# ---------------------------------------------------------------------------
+# BaseMessage helpers
+# ---------------------------------------------------------------------------
+
+
+class TestBaseMessage:
+    def test_system_message_role(self):
+        m = SystemMessage("hi")
+        assert m["role"] == "system"
+
+    def test_human_message_role(self):
+        m = HumanMessage("hi")
+        assert m["role"] == "user"
+
+    def test_ai_message_role(self):
+        m = AIMessage("hi")
+        assert m["role"] == "assistant"
+
+    def test_invalid_kwarg_raises(self):
+        with pytest.raises(ValueError, match="Invalid attributes"):
+            BaseMessage(role="user", content="x", bad_kwarg=True)
+
+    def test_str_with_string_content(self):
+        m = BaseMessage(role="user", content="hello")
+        assert str(m) == "hello"
+
+    def test_str_with_list_content(self):
+        m = BaseMessage(
+            role="user",
+            content=[
+                {"type": "text", "text": "a"},
+                {"type": "text", "text": "b"},
+            ],
+        )
+        assert str(m) == "a\nb"
+
+    def test_to_markdown_string_content(self):
+        m = BaseMessage(role="user", content="code")
+        md = m.to_markdown()
+        assert "```" in md
+        assert "code" in md
+
+
+# ---------------------------------------------------------------------------
+# extract_html_tags
+# ---------------------------------------------------------------------------
+
+
+class TestExtractHtmlTags:
+    def test_single_key(self):
+        text = "<action>click(5)</action>"
+        result = extract_html_tags(text, ["action"])
+        assert result == {"action": ["click(5)"]}
+
+    def test_multiple_matches(self):
+        text = "<a>1</a> <a>2</a>"
+        result = extract_html_tags(text, ["a"])
+        assert result == {"a": ["1", "2"]}
+
+    def test_missing_key_returns_empty(self):
+        text = "<a>1</a>"
+        result = extract_html_tags(text, ["b"])
+        assert result == {}
+
+    def test_multiline_content(self):
+        text = "<thought>\nline1\nline2\n</thought>"
+        result = extract_html_tags(text, ["thought"])
+        assert len(result["thought"]) == 1
+        assert "line1" in result["thought"][0]
+        assert "line2" in result["thought"][0]
+
+
+# ---------------------------------------------------------------------------
+# parse_html_tags
+# ---------------------------------------------------------------------------
+
+
+class TestParseHtmlTags:
+    def test_all_keys_present(self):
+        text = "<action>click</action><thought>reason</thought>"
+        content, valid, msg = parse_html_tags(
+            text, keys=("action", "thought")
+        )
+        assert valid is True
+        assert content["action"] == "click"
+        assert content["thought"] == "reason"
+
+    def test_missing_required_key(self):
+        text = "<action>click</action>"
+        content, valid, msg = parse_html_tags(
+            text, keys=("action", "thought")
+        )
+        assert valid is False
+        assert "thought" in msg
+
+    def test_optional_key_missing_still_valid(self):
+        text = "<action>click</action>"
+        content, valid, msg = parse_html_tags(
+            text, keys=("action",), optional_keys=("thought",)
+        )
+        assert valid is True
+
+    def test_duplicate_key_without_merge(self):
+        text = "<a>1</a><a>2</a>"
+        content, valid, msg = parse_html_tags(text, keys=("a",))
+        assert valid is False
+        assert "multiple" in msg.lower()
+
+    def test_duplicate_key_with_merge(self):
+        text = "<a>1</a><a>2</a>"
+        content, valid, msg = parse_html_tags(
+            text, keys=("a",), merge_multiple=True
+        )
+        assert valid is True
+        assert content["a"] == "1\n2"
+
+
+# ---------------------------------------------------------------------------
+# parse_html_tags_raise
+# ---------------------------------------------------------------------------
+
+
+class TestParseHtmlTagsRaise:
+    def test_raises_on_missing_key(self):
+        with pytest.raises(ParseError):
+            parse_html_tags_raise("<a>1</a>", keys=("a", "b"))
+
+    def test_returns_dict_on_success(self):
+        result = parse_html_tags_raise("<a>1</a>", keys=("a",))
+        assert result == {"a": "1"}