Last week, we had the author of TDD for a Shopping Website LiveProject. Friday at 11am Ranch time, Steven Solomon will be hosting a live TDD session just for us. See for the agenda and registration link
There might be a tomcat setting for limiting this but it seems easier to limit the upload size in your app. It is likely that you have a loop that is reading bytes from the incoming stream. You can just keep a sum of the size you've read so far and then throw an error if the size is greater than your threshold.
An advantage of doing this yourself instead of having tomcat do it is that your app is a little more portable. You can move it to another servlet container without worrying about the upload size limiting.