Add regression test

tests/test_memory.py

@@ -89,6 +89,28 @@ def test_action_step_to_messages():
     assert "image" in image_content
 
 
+def test_action_step_to_messages_no_tool_calls_with_observations():
+    action_step = ActionStep(
+        model_input_messages=None,
+        tool_calls=None,
+        start_time=None,
+        end_time=None,
+        step_number=None,
+        error=None,
+        duration=None,
+        model_output_message=None,
+        model_output=None,
+        observations="This is an observation.",
+        observations_images=None,
+        action_output=None,
+    )
+    messages = action_step.to_messages()
+    assert len(messages) == 1
+    observation_message = messages[0]
+    assert observation_message["role"] == MessageRole.TOOL_RESPONSE
+    assert "Observation:\nThis is an observation." in observation_message["content"][0]["text"]
+
+
 def test_planning_step_to_messages():
     planning_step = PlanningStep(
         model_input_messages=[Message(role=MessageRole.USER, content="Hello")],