diff --git a/test_stream_agent.py b/test_stream_agent.py
index 901a0a2..f3d2cb8 100644
--- a/test_stream_agent.py
+++ b/test_stream_agent.py
@@ -1,18 +1,24 @@
-from stream_agent import StreamingAIAgent
+from langchain_core.messages import AIMessage
+
+from stream_agent import format_message
 
 
-def test_stream_returns_chunks(monkeypatch):
-    monkeypatch.delenv("OPENAI_API_KEY", raising=False)
-    agent = StreamingAIAgent()
+def test_format_message_with_content():
+    message = AIMessage(content="hello")
 
-    chunks = list(agent.stream("test question"))
-
-    assert len(chunks) > 3
-    assert "".join(chunks).strip()
+    assert format_message(message) == "hello"
 
 
-def test_invoke_matches_stream(monkeypatch):
-    monkeypatch.delenv("OPENAI_API_KEY", raising=False)
-    agent = StreamingAIAgent()
+def test_format_message_with_tool_call():
+    message = AIMessage(
+        content="",
+        tool_calls=[
+            {
+                "name": "get_demo_price",
+                "args": {"product": "молоко", "city": "Казань"},
+                "id": "call-1",
+            }
+        ],
+    )
 
-    assert agent.invoke("hello") == "".join(agent.stream("hello"))
+    assert "get_demo_price" in format_message(message)