A friend was initially diagnosed with kidney stones but it is now being suggested that its an internal tear. What tests would determine this?

Nonsense. I have no understanding of an internal tear. Get to a urologist for a proper evaluation with a good history, physical exam and urinalysis. Your urologist will choose an imaging modality.
Imaging. I'm not sure what you mean by an "internal tear." the best way to diagose a kidney stone is either with ultrasound or a ct scan. An ultrasound will not identify ureteral stones. , so in some circumstances a ct scan is a better test. Your friends physician will have determined which test to obtain.