feat: update chat backend to use stub and add websocket chat service tests

tests/api/test_chat_ws.py

@@ -0,0 +1,124 @@
+"""Tests for the websocket chat service using the local stub agent.
+
+Uses Starlette's synchronous ``TestClient`` websocket support (rather than
+the ``httpx.AsyncClient`` fixture used elsewhere) since it triggers the
+FastAPI lifespan on ``__enter__``/``__exit__``, wiring up
+``app.chat_agent`` / ``app.state.chat_sessions`` exactly like a real
+server run.
+"""
+
+import pytest
+from fastapi.testclient import TestClient
+
+from app.main import app
+
+pytestmark = pytest.mark.anyio
+
+
+async def test_chat_ws_full_conversation_flow() -> None:
+    with (
+        TestClient(app) as client,
+        client.websocket_connect("/v1/chat/ws") as websocket,
+    ):
+        # 1. connect
+        connected = websocket.receive_json()
+        assert connected["type"] == "connected"
+        session_id = connected["session_id"]
+
+        # 2. start conversation with a system prompt
+        websocket.send_json(
+            {"type": "start", "system_prompt": "You are a helpful assistant."}
+        )
+        started = websocket.receive_json()
+        print(f"{started=}")
+        assert started == {"type": "started", "session_id": session_id}
+
+        # 3. send a user message and aggregate the streamed assistant chunks
+        websocket.send_json({"type": "user_message", "content": "hello"})
+
+        event = websocket.receive_json()
+        aggregated = ""
+        while event["type"] == "assistant_chunk":
+            assert event["index"] >= 0
+            aggregated += event["content"]
+            event = websocket.receive_json()
+
+        assert event["type"] == "assistant_message"
+        assert event["message"]["role"] == "assistant"
+        assert event["message"]["content"] == aggregated
+        print(f"{event=}")
+        print(f"{aggregated=}")
+        assert "hello" in aggregated.lower()
+
+        # 4. request full history (system + user + assistant)
+        websocket.send_json({"type": "history_request"})
+        history = websocket.receive_json()
+        assert history["type"] == "history"
+        roles = [m["role"] for m in history["messages"]]
+        assert roles == ["system", "user", "assistant"]
+
+        # 5. gracefully end the conversation
+        websocket.send_json({"type": "end"})
+
+
+async def test_chat_ws_invalid_event_returns_error() -> None:
+    with (
+        TestClient(app) as client,
+        client.websocket_connect("/v1/chat/ws") as websocket,
+    ):
+        websocket.receive_json()  # connected
+
+        websocket.send_json({"type": "not_a_real_event"})
+        error = websocket.receive_json()
+        assert error["type"] == "error"
+
+        websocket.send_json({"type": "end"})
+
+
+async def test_chat_ws_ask_question_and_print_model_answer() -> None:
+    """Ask a real question over the websocket chat and print the model's answer.
+
+    Runs against whatever ``ChatAgent`` is wired up via ``app.state.chat_agent``
+    (the local stub agent by default, or a real Ollama-backed agent when
+    ``CHAT_BACKEND=ollama`` is configured), exercising the full websocket
+    conversation flow end-to-end.
+    """
+    question = "What is the capital of France?"
+
+    with (
+        TestClient(app) as client,
+        client.websocket_connect("/v1/chat/ws") as websocket,
+    ):
+        # 1. connect
+        connected = websocket.receive_json()
+        assert connected["type"] == "connected"
+        session_id = connected["session_id"]
+
+        # 2. start conversation
+        websocket.send_json(
+            {"type": "start", "system_prompt": "You are a helpful assistant."}
+        )
+        started = websocket.receive_json()
+        assert started == {"type": "started", "session_id": session_id}
+
+        # 3. ask the question and aggregate the streamed answer
+        websocket.send_json({"type": "user_message", "content": question})
+
+        event = websocket.receive_json()
+        answer = ""
+        while event["type"] == "assistant_chunk":
+            answer += event["content"]
+            event = websocket.receive_json()
+
+        assert event["type"] == "assistant_message"
+        answer = event["message"]["content"]
+
+        print(f"\nQuestion: {question}")
+        print(f"Model answer: {answer}")
+
+        assert isinstance(answer, str)
+        assert answer.strip() != ""
+
+        # 4. gracefully end the conversation
+        websocket.send_json({"type": "end"})
+