It is just a quick & dirty way to check if “function decompilation” works.
RegExp.prototype.test method will take the argument and it will convert it to String, the
xyz reference inside the function is never evaluated.
Why would you have to check this?
Function.prototype.toString method returns an implementation-dependent representation of a function, and in some implementation, such older Safari versions, Mobile Opera, and some Blackberry browsers, they don’t actually return anything useful.