diff --git a/libs/core/tests/unit_tests/messages/test_utils.py b/libs/core/tests/unit_tests/messages/test_utils.py
index f0a5de99d4f..95344f58145 100644
--- a/libs/core/tests/unit_tests/messages/test_utils.py
+++ b/libs/core/tests/unit_tests/messages/test_utils.py
@@ -965,13 +965,13 @@ def test_convert_to_openai_messages_developer() -> None:
     result = convert_to_openai_messages(messages)
     assert result == [{"role": "developer", "content": "a"}] * 2
 
+
 def test_trim_messages_custom_counter() -> None:
     def dummy_token_counter(messages: list[BaseMessage]) -> int:
         # treat each message like it adds 3 default tokens at the beginning
         # of the message and at the end of the message. 3 + 4 + 3 = 10 tokens
         # per message.
 
-        default_content_len = 4
         default_msg_prefix_len = 3
         default_msg_suffix_len = 3
 
@@ -980,9 +980,13 @@ def test_trim_messages_custom_counter() -> None:
             if isinstance(msg.content, str):
                 str_len = int(len(msg.content) / 3)
                 count += default_msg_prefix_len + str_len + default_msg_suffix_len
-            if isinstance(msg.content, list):
-                content = int(len(msg.content[0]["text"]) / 3)
+            elif isinstance(msg.content, list):
+                content = int(len(msg.content[0]["text"]))
                 count += default_msg_prefix_len + content + default_msg_suffix_len
+            else:
+                msg = "Invalid message content"
+                raise TypeError(msg)
+
         return count
 
     messages = [