I got some work on a new project so I ran the 500, or so, unit tests and it took almost 3 minutes. Everything was mocked and no external dependencies so I got curious as to how on earth they could take so long.

I found some suspicious code doing a while loop over a date range incrementing by 1 day each time. It turned out the tests didn't initialise the start date which defaults to 01/01/0001, and there are 5 scenarios!

I got test execution down to a respectful 10s.