feat(handlers): add reasoning text to callback handler and related tests

.gitignore

@@ -7,3 +7,4 @@ __pycache__*
 .pytest_cache
 .ruff_cache
 *.bak
+.vscode

src/strands/handlers/callback_handler.py

@@ -17,15 +17,19 @@ def __call__(self, **kwargs: Any) -> None:
 
         Args:
             **kwargs: Callback event data including:
-
-                - data (str): Text content to stream.
-                - complete (bool): Whether this is the final chunk of a response.
-                - current_tool_use (dict): Information about the current tool being used.
+            - reasoningText (Optional[str]): Reasoning text to print if provided.
+            - data (str): Text content to stream.
+            - complete (bool): Whether this is the final chunk of a response.
+            - current_tool_use (dict): Information about the current tool being used.
         """
+        reasoningText = kwargs.get("reasoningText", False)
         data = kwargs.get("data", "")
         complete = kwargs.get("complete", False)
         current_tool_use = kwargs.get("current_tool_use", {})
 
+        if reasoningText:
+            print(reasoningText, end="")
+
         if data:
             print(data, end="" if not complete else "\n")
 

tests/strands/handlers/test_callback_handler.py

@@ -30,6 +30,31 @@ def test_call_with_empty_args(handler, mock_print):
     mock_print.assert_not_called()
 
 
+def test_call_handler_reasoningText(handler, mock_print):
+    """Test calling the handler with reasoningText."""
+    handler(reasoningText="This is reasoning text")
+    # Should print reasoning text without newline
+    mock_print.assert_called_once_with("This is reasoning text", end="")
+
+
+def test_call_without_reasoningText(handler, mock_print):
+    """Test calling the handler without reasoningText argument."""
+    handler(data="Some output")
+    # Should only print data, not reasoningText
+    mock_print.assert_called_once_with("Some output", end="")
+
+
+def test_call_with_reasoningText_and_data(handler, mock_print):
+    """Test calling the handler with both reasoningText and data."""
+    handler(reasoningText="Reasoning", data="Output")
+    # Should print reasoningText and data, both without newline
+    calls = [
+        unittest.mock.call("Reasoning", end=""),
+        unittest.mock.call("Output", end=""),
+    ]
+    mock_print.assert_has_calls(calls)
+
+
 def test_call_with_data_incomplete(handler, mock_print):
     """Test calling the handler with data but not complete."""
     handler(data="Test output")