feat: Add test for reasoning content formatting in Coder.send() method

tests/basic/test_reasoning.py

@@ -0,0 +1,59 @@
+import unittest
+from unittest.mock import MagicMock, patch
+
+from aider.coders.base_coder import Coder
+from aider.io import InputOutput
+from aider.models import Model
+from aider.reasoning_tags import REASONING_TAG, format_reasoning_content, replace_reasoning_tags
+
+
+class TestReasoning(unittest.TestCase):
+    def test_send_with_reasoning_content(self):
+        """Test that reasoning content is properly formatted and output."""
+        # Setup IO with no streaming, no pretty
+        io = InputOutput(pretty=False, stream=False)
+        io.ai_output = MagicMock()
+        
+        # Setup model and coder
+        model = Model("gpt-3.5-turbo")
+        coder = Coder.create(model, None, io=io)
+        
+        # Test data
+        reasoning_content = "My step-by-step reasoning process"
+        main_content = "Final answer after reasoning"
+        
+        # Mock completion response with reasoning content
+        class MockCompletion:
+            def __init__(self, content, reasoning_content):
+                self.content = content
+                self.reasoning_content = reasoning_content
+        
+        mock_completion = MockCompletion(main_content, reasoning_content)
+        
+        # Mock the model's send_completion method
+        with patch.object(model, 'send_completion', return_value=mock_completion):
+            # Call send with a simple message
+            messages = [{"role": "user", "content": "test prompt"}]
+            coder.send(messages)
+            
+            # Check if ai_output was called with formatted content
+            io.ai_output.assert_called_once()
+            output = io.ai_output.call_args[0][0]
+            
+            # Output should contain formatted reasoning tags
+            self.assertIn("Thinking ...", output)
+            self.assertIn("... done thinking", output)
+            
+            # Output should include both reasoning and main content
+            self.assertIn(reasoning_content, output)
+            self.assertIn(main_content, output)
+            
+            # Ensure proper order: reasoning first, then main content
+            reasoning_pos = output.find(reasoning_content)
+            main_pos = output.find(main_content)
+            self.assertLess(reasoning_pos, main_pos, 
+                           "Reasoning content should appear before main content")
+
+
+if __name__ == "__main__":
+    unittest.main()