Urgh. I recently had a similar situation. I started interviewing with a company who have a take-home assignment which I could have completed in the required time without taking any care over the quality of code I was submitting, but to do it properly I spent a bit of time thinking about it and building a reasonably extensive test-suite along the way.

I was asked to come in for a face to face interview, for which I made clear I was having to take a day off of work, which was cancelled a few working hours before (so I wasn't able to cancel the holiday) without an apology. I was then interviewed again by phone and told that there was 'a bug' in my code and that I should try to find it and resubmit it without any other details. The spec was a puzzle with lots of weird edge cases and horrible inconsistencies.

I decided at that point that I didn't want to work with them.