ClockSourceMock is a StaticImmortal under the hood, so it is shared by all unittests within a given process. This means that tests can observe state from prior test runs, in particular any alarms registered by previous tests. These alarms in theory could contain data that has since been deallocated, or clashes with the new hasAlarmAt functionality could occur. We should at least reset the mock clock between test runs, or preferably use separate instances of it altogether per ServiceContext.