Michael J. Swart says, look at the time!:
A flaky test is a unit test that sometimes passes and sometimes fails. The causes of these flaky tests are often elusive because they’re not consistently reproducible.
I’ve found that unit tests that deal with dates and times are notorious for being flaky – especially such tests that talk to SQL Server. I want to explore some of the reasons this can happen.
As a quick note, if you’re using time in database unit tests, don’t use GETUTCDATE() or GETDATE() or any other function like that. It’s a non-deterministic function. Instead, use specific dates and times. That way, you can explicitly test for the types of things Michael points out.