Failing a teststep using context class

I am using pro version and I want to fail a teststep which has a script assertion.

I am aware that I can use testRunner.fail() function to fail a teststep in groovy but testRunner class doesn't have scope in script assertion. Only context,log and messageExchange classes has scope over there.

Please share is you have any idea about it.

Cheers,

Varun