swifi fault injection command

I'm adding some new module in Minix 3, and I want to check if the new module affect the self repairing property of the minix 3 .

i read that i can use swifi injection tool to fire some failure in drivers.but i guess i'am not able to use it in a correct way,for example when i run command like: "swifi -f /usr/sbin/dp8390 5 Ransom_fault 5 20"

it reurns :

• fault_injection_returned 0 (0)
• 0 failure and 0 error

can anyone help me ,how to use swifi or what is wrong with the command i typed.