[Rannath]

You don't test your renderer. The renderer is third party tech in 99% of games. You test that the right calls are being made to the renderer. For that you use a mock. Your test are there to assert correctness in YOUR code. if something exists outside your code you test it another way.

Example: Sam is writing an engine. He has OpenGL, DX9, and DX11 bindings. He also has a Mock that logs calls and checks to see that they match known good logs. Sam then sets up a demo to cycle through all the different graphical capabilities of his engine, this also gives Sam the ability to test his AI/scene crafting code.