You can check in www.mcu.cz to download the file : testbench.pdf. The size of file is large so I can not upload into eda site. If you search nothing, please let me know I can check for you.
testbench is a kind of similation for hardware design. By use testbench file you can check you design more exactly about waveform, real-time response so you should pay attenion to it.
Hope to discuss about this problem
Best regard