Making a Midterm is No Fun

I think one of most challenging parts of teaching a course is setting up exams. 

There are a lot of constraints:

You want to cover, as reasonably as possible, all the material.
You want to target somewhere around the median of the class;  not too hard, not too easy. 
You don't want there to be any severe typos or other problems with problem;  you can't have a problem without a solution or is otherwise confusing.  
There are a limited number of good problems readily available;  making up new problems is challenging.  (Again, you don't want errors...)
You have to make it all do-able in 90 minutes.  
And so on....

I look forward to reaching a point where I don't think it's worth giving exams to students.  (I don't in my grad classes.)  For my undergrad class, I still think it's necessary.