阶段3（上）：Python/asyncio/FastAPI 专题的课程、企业场景、面试题和可运行示例

topics/python/fastapi/examples/chat-api/test_app.py

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+# requires: fastapi, httpx
+import json
+from collections.abc import AsyncIterator
+
+from fastapi.testclient import TestClient
+
+from app import Message, app, get_llm
+
+AUTH = {"X-API-Key": "demo-key"}
+BODY = {"messages": [{"role": "user", "content": "你好"}]}
+
+
+class ScriptedLLM:
+    """测试替身：按脚本返回 token，可以模拟中途失败。"""
+
+    def __init__(self, tokens: list[str], fail_at: int | None = None) -> None:
+        self.tokens, self.fail_at = tokens, fail_at
+        self.calls: list[list[Message]] = []
+
+    async def stream(self, messages: list[Message], temperature: float) -> AsyncIterator[str]:
+        self.calls.append(messages)
+        for i, t in enumerate(self.tokens):
+            if i == self.fail_at:
+                raise RuntimeError("上游模型 500")
+            yield t
+
+
+def client_with(llm) -> TestClient:
+    app.dependency_overrides[get_llm] = lambda: llm
+    return TestClient(app, raise_server_exceptions=False)
+
+
+def parse_sse(text: str) -> list[tuple[str, str]]:
+    events = []
+    for block in text.strip().split("\n\n"):
+        name, data = "message", ""
+        for line in block.splitlines():
+            if line.startswith("event: "):
+                name = line[7:]
+            elif line.startswith("data: "):
+                data = line[6:]
+        events.append((name, data))
+    return events
+
+
+def teardown_function():
+    app.dependency_overrides.clear()
+
+
+def test_auth_required():
+    r = client_with(ScriptedLLM(["x"])).post("/v1/chat", json=BODY)
+    assert r.status_code == 401 and r.json()["code"] == "HTTP_401" and r.json()["request_id"]
+
+
+def test_validation_error_format():
+    r = client_with(ScriptedLLM(["x"])).post("/v1/chat", headers=AUTH,
+                                             json={"messages": [{"role": "robot", "content": ""}], "temperature": 5})
+    assert r.status_code == 422
+    fields = {d["field"] for d in r.json()["details"]}
+    assert {"messages.0.role", "messages.0.content", "temperature"} <= fields
+
+
+def test_non_stream():
+    llm = ScriptedLLM(["你", "好"])
+    r = client_with(llm).post("/v1/chat", headers={**AUTH, "X-Request-ID": "rid-1"}, json={**BODY, "stream": False})
+    assert r.status_code == 200
+    assert r.json() == {"request_id": "rid-1", "content": "你好"}
+    assert r.headers["X-Request-ID"] == "rid-1"
+    assert llm.calls[0][0].content == "你好"
+
+
+def test_stream_sse():
+    r = client_with(ScriptedLLM(["A", "B", "C"])).post("/v1/chat", headers=AUTH, json=BODY)
+    assert r.status_code == 200 and r.headers["content-type"].startswith("text/event-stream")
+    events = parse_sse(r.text)
+    assert [json.loads(d)["delta"] for n, d in events[:-1]] == ["A", "B", "C"]
+    assert events[-1] == ("message", "[DONE]")
+
+
+def test_stream_error_event():
+    r = client_with(ScriptedLLM(["A", "B"], fail_at=1)).post("/v1/chat", headers=AUTH, json=BODY)
+    events = parse_sse(r.text)
+    assert events[0][0] == "message" and events[-1][0] == "error"
+    assert json.loads(events[-1][1])["message"] == "生成失败"
+
+
+def test_internal_error_hides_details():
+    r = client_with(ScriptedLLM([])).get("/boom")
+    assert r.status_code == 500
+    assert r.json()["message"] == "服务器内部错误" and "postgres" not in r.text