v2.0 补充单元测试，行覆盖90以上

src/mvp/py/tests/test_db.py

@@ -0,0 +1,42 @@
+from __future__ import annotations
+
+from pathlib import Path
+
+
+def test_db_lifecycle_and_basic_queries(tmp_path: Path):
+    from argus.service.db import Db
+
+    db = Db(str(tmp_path / "mvp.sqlite3"))
+    db.init()
+
+    t = db.create_task(
+        task_id="t1",
+        workload="ppo",
+        jobspec_yaml="workload: ppo\ncode_path: /c\nmodel_id: m\ntrain_file: t\n",
+        nnodes=2,
+        n_gpus_per_node=4,
+    )
+    assert t["task_id"] == "t1"
+    assert db.get_task("t1") is not None
+
+    q = db.list_queue()
+    assert len(q["pending"]) == 1
+
+    db.set_task_state(task_id="t1", state="PENDING_RESOURCES", next_run_at="2099-01-01T00:00:00Z")
+    assert db.pick_next_runnable_task() is None
+
+    # next_run_at is sticky unless explicitly updated; a future value keeps it non-runnable.
+    db.set_task_state(task_id="t1", state="QUEUED", next_run_at=None)
+    assert db.pick_next_runnable_task() is None
+
+    # Allow it by setting next_run_at into the past.
+    db.set_task_state(task_id="t1", state="QUEUED", next_run_at="2000-01-01T00:00:00Z")
+    assert db.pick_next_runnable_task() is not None
+
+    db.create_attempt(task_id="t1", attempt_no=1, ray_submission_id="sid1")
+    db.update_attempt(task_id="t1", attempt_no=1, ray_status="RUNNING")
+    attempts = db.list_attempts("t1")
+    assert attempts[-1]["ray_status"] == "RUNNING"
+
+    # No-op update is allowed
+    db.update_attempt(task_id="t1", attempt_no=1)