A test is always a good way to get to know the procedure .
Just be carefull to understand the purpose of it .
growth rate depends on many factors :
-size of the procedure because previous study showed that the growth rate may decrease with increasing grafting density per surface unit .
-during surgery , grafts are exposed to the air and cells metabolism outside the body could generate what they call free radical oxygen that could impair the growth .
some clinics use normal saline solution but others prefer to use antioxydants media such as hypothermosol .
Independant factors such as another big surgery after your HT , a serious disease may also affect the final results ,etc...
If you want to do the test to get familiar with the procedure ( anesthesia , placing , cutting grafts ,etc...) , it is OK .Make sure they will do the test at the same density they are planning to do all over the place to get as close as possible to reality .
Otherwise ,the growth you will have may not be reproducible when they will do a big procedure .
Do the test to alleviate the anxiety related to the surgery and it's unknown but not to assess the growth rate because many others factors could make it irrelevant .