Check to make sure a line of code ran successfully

how do I confirm this a solidity line of code ran successfully

claimed[msg.sender] = claimed[msg.sender].add(1); // make sure this goes first before transfer to prevent reentrancy

this seems like a simple line of code, it should run successfully when it is executed

the comment there seems to be to run it before a transfer so that someone can not make the transfer multiple times without changing that value