diff --git a/tests/agents/test_tool_use_agent_discussion.py b/tests/agents/test_tool_use_agent_discussion.py
new file mode 100644
index 000000000..ca2eed6b6
--- /dev/null
+++ b/tests/agents/test_tool_use_agent_discussion.py
@@ -0,0 +1,128 @@
+from agentlab.agents.tool_use_agent.tool_use_agent import StructuredDiscussion
+from agentlab.llm.response_api import AnthropicAPIMessageBuilder
+
+
+def make_msg(text: str) -> AnthropicAPIMessageBuilder:
+    msg = AnthropicAPIMessageBuilder("user").add_text(text)
+    msg._cache_breakpoint = False
+    return msg
+
+
+def make_discussion(n_groups: int, n_msg_per_group: int = 2, with_summary: bool = True, **kwargs):
+    discussion = StructuredDiscussion(**kwargs)
+    for i in range(n_groups):
+        discussion.new_group(f"group_{i}")
+        for j in range(n_msg_per_group):
+            discussion.append(make_msg(f"msg_{i}_{j}"))
+        if with_summary:
+            discussion.set_last_summary(make_msg(f"summary_{i}"))
+    return discussion
+
+
+def texts(messages):
+    return [msg.content[0]["text"] for msg in messages]
+
+
+def breakpoints(messages):
+    return [getattr(msg, "_cache_breakpoint", False) for msg in messages]
+
+
+def test_new_group_and_append():
+    discussion = StructuredDiscussion()
+    assert not discussion.is_goal_set()
+    assert discussion.get_last_summary() is None
+
+    discussion.new_group()
+    discussion.append(make_msg("a"))
+    discussion.append(make_msg("b"))
+
+    assert discussion.is_goal_set()
+    assert discussion.groups[0].name == "group_0"
+    assert texts(discussion.groups[0].messages) == ["a", "b"]
+    assert discussion.get_last_summary() is None
+
+    summary = make_msg("summary")
+    discussion.set_last_summary(summary)
+    assert discussion.get_last_summary() is summary
+
+
+def test_flatten_empty_discussion():
+    assert StructuredDiscussion().flatten() == []
+
+
+def test_flatten_without_keep_last_n_obs_keeps_everything():
+    discussion = make_discussion(3)
+
+    messages = discussion.flatten()
+
+    assert texts(messages) == [f"msg_{i}_{j}" for i in range(3) for j in range(2)]
+    assert breakpoints(messages) == [True, False, False, False, False, False]
+
+
+def test_flatten_replaces_non_tail_groups_by_their_summary():
+    discussion = make_discussion(4, keep_last_n_obs=2)
+
+    messages = discussion.flatten()
+
+    assert texts(messages) == [
+        "summary_0",
+        "summary_1",
+        "msg_2_0",
+        "msg_2_1",
+        "msg_3_0",
+        "msg_3_1",
+    ]
+    # the tail starts at group index 2, and the breakpoint is set on the message at that index
+    assert breakpoints(messages) == [False, False, True, False, False, False]
+
+
+def test_flatten_keeps_only_last_group_verbatim():
+    discussion = make_discussion(3, keep_last_n_obs=1)
+
+    messages = discussion.flatten()
+
+    assert texts(messages) == ["summary_0", "summary_1", "msg_2_0", "msg_2_1"]
+    assert breakpoints(messages) == [False, False, True, False]
+
+
+def test_flatten_falls_back_on_messages_when_group_has_no_summary():
+    discussion = make_discussion(3, keep_last_n_obs=1, with_summary=False)
+    discussion.groups[1].summary = make_msg("summary_1")
+
+    messages = discussion.flatten()
+
+    assert texts(messages) == ["msg_0_0", "msg_0_1", "summary_1", "msg_2_0", "msg_2_1"]
+    assert breakpoints(messages) == [False, False, True, False, False]
+
+
+def test_flatten_unsets_previous_cache_breakpoints():
+    discussion = make_discussion(3, keep_last_n_obs=1)
+    for group in discussion.groups:
+        group.summary._cache_breakpoint = True
+        for msg in group.messages:
+            msg._cache_breakpoint = True
+
+    messages = discussion.flatten()
+
+    assert breakpoints(messages) == [False, False, True, False]
+
+
+def test_flatten_keep_last_n_obs_larger_than_number_of_groups():
+    discussion = make_discussion(2, keep_last_n_obs=5)
+
+    messages = discussion.flatten()
+
+    assert texts(messages) == ["msg_0_0", "msg_0_1", "msg_1_0", "msg_1_1"]
+    assert breakpoints(messages) == [False, False, False, False]
+
+
+def test_flatten_moves_breakpoint_when_a_group_is_added():
+    discussion = make_discussion(3, keep_last_n_obs=2)
+    assert breakpoints(discussion.flatten()) == [False, True, False, False, False]
+
+    discussion.new_group()
+    discussion.append(make_msg("msg_3_0"))
+
+    messages = discussion.flatten()
+    assert texts(messages) == ["summary_0", "summary_1", "msg_2_0", "msg_2_1", "msg_3_0"]
+    assert breakpoints(messages) == [False, False, True, False, False]