feat: implement mvp with email-first login flow and langgraph architecture

tests/test_logging_langchain.py

@@ -0,0 +1,64 @@
+import logging
+import pytest
+import io
+from unittest.mock import MagicMock
+from ea_chatbot.utils.logging import LangChainLoggingHandler
+
+@pytest.fixture
+def log_capture():
+    """Fixture to capture logs from a logger."""
+    log_stream = io.StringIO()
+    logger = logging.getLogger("test_langchain")
+    logger.setLevel(logging.INFO)
+    # Remove existing handlers
+    for handler in logger.handlers[:]:
+        logger.removeHandler(handler)
+    
+    handler = logging.StreamHandler(log_stream)
+    logger.addHandler(handler)
+    return logger, log_stream
+
+def test_langchain_logging_handler_on_llm_start(log_capture):
+    """Test that on_llm_start logs the correct message."""
+    logger, log_stream = log_capture
+    handler = LangChainLoggingHandler(logger=logger)
+    handler.on_llm_start(serialized={"name": "test_model"}, prompts=["test prompt"])
+    
+    output = log_stream.getvalue()
+    assert "LLM Started:" in output
+    assert "test_model" in output
+
+def test_langchain_logging_handler_on_llm_end(log_capture):
+    """Test that on_llm_end logs token usage."""
+    logger, log_stream = log_capture
+    handler = LangChainLoggingHandler(logger=logger)
+    response = MagicMock()
+    response.llm_output = {
+        "token_usage": {
+            "prompt_tokens": 10,
+            "completion_tokens": 20,
+            "total_tokens": 30
+        },
+        "model_name": "test_model"
+    }
+    
+    handler.on_llm_end(response=response)
+    
+    output = log_stream.getvalue()
+    assert "LLM Ended:" in output
+    assert "test_model" in output
+    assert "Tokens: 30" in output
+    assert "10 prompt" in output
+    assert "20 completion" in output
+
+def test_langchain_logging_handler_on_llm_error(log_capture):
+    """Test that on_llm_error logs the error."""
+    logger, log_stream = log_capture
+    handler = LangChainLoggingHandler(logger=logger)
+    error = Exception("test error")
+    
+    handler.on_llm_error(error=error)
+    
+    output = log_stream.getvalue()
+    assert "LLM Error:" in output
+    assert "test error" in output