FRC Sim
FRC Sim was made to test code when the robot to test the code on was unavalable. I would say that the programmers on my team would get about a week or two to properly test code on a mostly finished robot and that was assuming that the robot didn't encounter any damage or unintended effects from testing. The robot model used in the sim was taken from the CAD file of the finished robot and integrated with code used by the simulator. The simulator utilizes the network table created from the C++ code that is used to control the robot and grabs specific values to make a rotational or linear movement. Since the robot had to first be imported to Unity in order to have code be applyed to moving or sliding joints, any model can be made as a representation of the robot or a custom made robot can be made from scratch and be controlled through the robot code.