pytest 写测试：不起日志代理，也能把值班助手测透

@WebMvcTest(GcController.class)
class GcControllerTest {
  @Autowired MockMvc mvc;
  @MockBean LogAgentClient agent;

  @Test void unknownServiceIs404() throws Exception {
    mvc.perform(get("/gc/summary")
         .param("service", "pay"))
       .andExpect(status().isNotFound());
  }
}

class TestParse(unittest.TestCase):
    def setUp(self):
        self.log = fake_log(12.0, 244.05)

    def test_max(self):
        h = parse("order-01", self.log)
        self.assertEqual(h.max_ms, 244.05)
        self.assertIsNone(h.error)

def test_max(agent_logs):
    h = parse("order-01", agent_logs["order-01"])
    assert h.max_ms == 244.05
    assert h.error is None

• 更老的办法是写个脚本 print 一下、肉眼看对不对：没法进 CI，改代码后也没人会重跑。
• unittest 能用，但样板多：类、继承、self.assertEqual，准备数据只能放在 setUp 里，粒度太粗。
• 缺的那一块就是这页的精华：按参数名注入、可组合、可指定作用域的 fixture，加上会“自己解释失败原因”的 assert。

本页学 pytest。测接口时还有一个选择：真起 uvicorn 再用 HTTP 打，还是用 TestClient 在进程里直接调。前者更像线上但慢、要管端口和进程；后者快、稳，覆盖第 2～9 站的全部逻辑。默认用 TestClient，真起服务的测试留给少量冒烟测试。

$ uv add --dev pytest pytest-cov
# 本机装到 pytest 9.2.0、pytest-cov 7.1.0；写进 pyproject 的 [dependency-groups] dev，不进生产依赖

[tool.pytest.ini_options]
pythonpath = ["."]        # 让 tests/ 里能 import main
testpaths = ["tests"]     # 只在 tests/ 下找测试

import httpx
import pytest
from fastapi.testclient import TestClient

import main

PAUSE_LINE = "[2026-11-08T20:05:00.000+0800][info][gc] GC(0) Pause Young (Normal) (G1 Evacuation Pause) 512M->128M(1024M) {ms}ms"

def fake_log(*ms: float) -> str:
    return "\n".join(PAUSE_LINE.format(ms=f"{m:.3f}") for m in ms)

@pytest.fixture
def agent_logs():
    """每个测试一份新的“日志代理数据”，测试里可以随便改。"""
    return {"order-01": fake_log(12.0, 244.05), "order-02": fake_log(80.4),
            "order-03": "", "order-04": None, "order-05": fake_log(41.0)}   # None = 卡住不回

@pytest.fixture
def client(agent_logs):
    async def handler(request: httpx.Request) -> httpx.Response:
        host = request.url.path.split("/")[1]
        if agent_logs[host] is None:
            raise httpx.ReadTimeout("agent hung", request=request)
        return httpx.Response(200, text=agent_logs[host])

    fake = httpx.AsyncClient(transport=httpx.MockTransport(handler), base_url="http://agent")
    main.app.dependency_overrides[main.get_client] = lambda: fake
    with TestClient(main.app) as c:          # with：会跑 lifespan
        yield c
    main.app.dependency_overrides.clear()     # 收尾：别让替身漏到别的测试

import pytest
from main import parse
from conftest import fake_log

def test_parse_counts_and_max():
    h = parse("order-01", fake_log(12.0, 244.05, 33.1))
    assert h.pauses == 3
    assert h.max_ms == 244.05
    assert h.avg_ms == pytest.approx(96.4, abs=0.05)

def test_parse_empty_log_is_not_an_error():
    h = parse("order-04", "")
    assert h.error == "no pauses"
    assert h.max_ms is None

@pytest.mark.parametrize("line, expected", [
    ("... Pause Young (Normal) (G1 Evacuation Pause) 512M->128M(1024M) 23.456ms", 1),
    ("... Pause Full (System.gc()) 900M->300M(1024M) 812.000ms", 1),
    ("... Using 8 workers of 8 for evacuation", 0),
    ("... Pause Young 23.456 ms", 0),               # 单位前多了空格，正则不认
])
def test_which_lines_count(line, expected):
    assert parse("h", line).pauses == expected

def test_summary_marks_hung_host(client):
    r = client.get("/gc/summary", params={"service": "order", "minutes": 10})
    assert r.status_code == 200
    hosts = {h["host"]: h for h in r.json()["hosts"]}
    assert hosts["order-01"]["max_ms"] == 244.05
    assert hosts["order-03"]["error"] == "no pauses"
    assert hosts["order-04"]["error"] is not None

def test_unknown_service_is_404(client):
    r = client.get("/gc/summary", params={"service": "pay"})
    assert r.status_code == 404
    assert r.json() == {"detail": "unknown service: pay"}

def test_minutes_out_of_range_is_422(client):
    r = client.get("/gc/summary", params={"service": "order", "minutes": 0})
    assert r.status_code == 422
    assert r.json()["detail"][0]["loc"] == ["query", "minutes"]

def test_agent_change_only_affects_this_test(client, agent_logs):
    agent_logs["order-02"] = ""
    r = client.get("/gc/order-02")
    assert r.json()["error"] == "no pauses"

$ uv run pytest -q
tests/test_api.py:2: 
E           httpx.ReadTimeout: agent hung
tests/conftest.py:23: ReadTimeout
FAILED tests/test_api.py::test_summary_marks_hung_host - httpx.ReadTimeout: a...
1 failed, 9 passed in 0.35s

    except TimeoutError:
        return HostGc(host=host, error="timeout 1s")
    except httpx.HTTPError as e:                  # httpx 自己的超时、连不上：也记成这一台出错
        return HostGc(host=host, error=type(e).__name__)

$ uv run pytest -v
tests/test_api.py::test_summary_marks_hung_host PASSED                   [ 10%]
tests/test_api.py::test_unknown_service_is_404 PASSED                    [ 20%]
tests/test_api.py::test_minutes_out_of_range_is_422 PASSED               [ 30%]
tests/test_api.py::test_agent_change_only_affects_this_test PASSED       [ 40%]
tests/test_parse.py::test_parse_counts_and_max PASSED                    [ 50%]
tests/test_parse.py::test_parse_empty_log_is_not_an_error PASSED         [ 60%]
tests/test_parse.py::test_which_lines_count[... Pause Young (Normal) (G1 Evacuation Pause) 512M->128M(1024M) 23.456ms-1] PASSED [ 70%]
tests/test_parse.py::test_which_lines_count[... Pause Full (System.gc()) 900M->300M(1024M) 812.000ms-1] PASSED [ 80%]
tests/test_parse.py::test_which_lines_count[... Using 8 workers of 8 for evacuation-0] PASSED [ 90%]
tests/test_parse.py::test_which_lines_count[... Pause Young 23.456 ms-0] PASSED [100%]
============================== 10 passed in 0.11s ==============================

$ uv run pytest -q --cov=main --cov-report=term-missing
Name      Stmts   Miss  Cover   Missing
main.py      67      3    96%   36, 57, 85

• 看参数化的 4 组各算一个测试，名字里带着参数，挂了一眼知道是哪一组。第 4 组故意写了个“单位前多一个空格”的行，确认正则不会误认。
• 看test_agent_change_only_affects_this_test 把 order-02 的日志改成空的。因为 agent_logs 是默认的 function 作用域，别的测试拿到的还是原来的数据。
• 看覆盖率 96%，没覆盖的三行各有原因：第 36 行是真的 get_client，被替身换掉了所以从没执行；第 57 行是 asyncio.timeout 那个分支，替身是立刻抛异常，没真等满 1 秒；第 85 行是 /healthz，没写测试。覆盖率只告诉你哪些行没跑过，不告诉你测得对不对。

实测 本机 uv 0.13.7、CPython 3.13.18、pytest 9.2.0、pytest-cov 7.1.0、FastAPI 0.162.2、httpx 0.28.1，输出逐字复制（失败输出只保留了关键几行，省略了 TestClient 的一条弃用警告）。10 个测试 0.11 s。