Agile methodologies aren't complicated things. They are, however, notoriously hard to do. We are only on our third scrum sprint and the issue of unit testing has raised its ugly head.
I get the impression that developers don't like writing unit tests. I imagine that they're not fun, that they feel like you're getting nothing done, making no progress toward those exciting deliverables, but one of the principles of agile development is that you have to do unit tests. It is the only way to make sure that you are delivering solid code at the end of these short development cycles. It's the sort of thing that gets done as you go, or it does not get done at all, because no one wants to take the time required to catch up when that time could be used to code another new feature--whether or not it works.
Here's a quick overview of agile concepts.