Hello,
The best way to test this is creating a shopping cart in saved status.
Then, put a breakpoint at this BAdI and execute function module BBP_PD_SC_TRANSFER, providing the cart header GUID as input parameter.
Breakpoint should stop now.
However, this BAdI will only be called if BBP_CREATE_BE_RQ_NEW is not activated, since this one is a new version of BBP_CREATE_REQ_BACK.
Regards,
Ricardo