diff --git a/test_stream_agent.py b/test_stream_agent.py
new file mode 100644
index 0000000..f3d2cb8
--- /dev/null
+++ b/test_stream_agent.py
@@ -0,0 +1,24 @@
+from langchain_core.messages import AIMessage
+
+from stream_agent import format_message
+
+
+def test_format_message_with_content():
+    message = AIMessage(content="hello")
+
+    assert format_message(message) == "hello"
+
+
+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 "get_demo_price" in format_message(message)