test: the app's clock never goes back in the test suite

The docker VM the suite runs in steps its wall clock back now and then (measured: 2 steps in 20 s, up to 0.5 s), so rows a test made one after another could read out of order (a files list sorted newest first, a scheduler's last runs). Every app module that took datetime from the datetime module reads a clock that never repeats or goes back; the scheduler test's own fixture for this goes.

backend/tests/test_scheduler.py

@@ -22,31 +22,6 @@ from app.runstatus import RunStatus, RunTrigger
 _JOB = "unit_test_claim"  # not a real job id — exercises the primitive without touching live jobs
 
 
-class _StrictlyLater(datetime):
-    """A clock that never repeats or goes back: each reading at least a microsecond after the last."""
-
-    last: datetime | None = None
-    clock: type[datetime] = datetime
-
-    @classmethod
-    def now(cls, tz=None):
-        t = cls.clock.now(tz)
-        if cls.last is not None and t <= cls.last:
-            t = cls.last + timedelta(microseconds=1)
-        cls.last = t
-        return t
-
-
-@pytest.fixture(autouse=True)
-def _runs_start_in_order(monkeypatch):
-    """Runs started in a row start in that order. These tests open several runs within microseconds
-    and read them back newest first, by start time; the wall clock of a container on a VM can step
-    back between two readings (seen: the third of three runs sorted before the second)."""
-    _StrictlyLater.last = None
-    _StrictlyLater.clock = jobruns.datetime
-    monkeypatch.setattr(jobruns, "datetime", _StrictlyLater)
-
-
 def _release():
     scheduler._record(_JOB, running=False)