You can find examples of how to run the specification test and calculate the rk-statistic right here. Look at example.do.
To be clear: I'm posting this code solely as an example of how the criteria might be calculated. It's here mainly to help readers better understand the criteria by seeing them computed in practice. Some readers may be tempted to apply the code directly to their own data. If you go that route just be aware that I provide this code as-is with no guarantee that it will deliver the estimates you want. It's your responsibility to make sure the code is doing what you expect.*