import json

from laya_router.feed import read_routes


def test_read_routes_keeps_the_tail(tmp_path):
    path = tmp_path / "routes.jsonl"
    lines = [json.dumps({"ts": str(i), "level": "simple"}) for i in range(5)]
    path.write_text("\n".join(lines) + "\nbad\n", encoding="utf-8")
    records = read_routes(path, limit=2)
    assert [item["ts"] for item in records] == ["3", "4"]