ABSTRACT
Physics engines usually rely on a collision mesh that is hand-crafted by artists. This meshes may have holes, bad normals, or other wrong data that might cause weird behavior at runtime. Testing those wrong behaviors manually has an extremely high cost in regards to manual testing. One small hole or bad normal can cause a character or vehicle to behave in a completely wrong manner, and those bugs are seldom reproduced because it might depend on many variables such as engine time step, character speed, and angle.
