Change a way of creating new dates in test.

Close #1242.

Previously every date in test was created by `new Date()`. 
Problem with this approach is that is not always true that `new Date() === new Date()` and `setDate` just set the day number. That's the reason that this test failed randomly. 
Can this be one lined to
numToDate = (x: number) => new Date(today.getTime()).setDate(today.getDate() + x)