I'm currently in the planning stage for my next game, and since I've been away from C++ for a while I have some questions about helpful libraries. I plan on making a 2D game with SDL, constructing my own simple 2D engine. I plan on making this game for the PC.

What libraries would you recommend to make this process easier?

What about unittests?

What about an enforce operator to throw exceptions?

int a = 1;
enforce(a == 2); //Throws an exception, 

Specifically, i'm looking for general purpose libraries, that implement that make my life easier (like boost). Also, a helpful library for physics/collision, AI, XML file parsing (specifically working with the Tiled map editor), and any others that you guys have used that are useful in a 2D game.