MVPs? Absolutely. Just because it's the first iteration doesn't mean it's not important to test that everything in that first iteration works.

Hobby projects? Less so, particularly if it's just me writing software. However, if I'm writing a particularly hairy piece of logic I'll absolutely write some tests for it (for example, I wrote a JS calendar plugin just to see if I could do better than the many existing ones, and I did all of the date logic myself using JS's terrible Date library).