Insert a print statement at the beginning of the function. It will print the random test case.

JS, unlike other langs such as Haskell, has no builtin lazy evaluation support
Which means all arguments will be evaluated before passing them to the function
Also, replace only takes two does not means other arguments will not be evaluated
So, given

(ExprA).Method((ExprB),(ExprC),(ExprD))

You can transform it into an equivalent form

RstA = ExprA
Method = RstA.Method
RstB = ExprB
RstC = ExprC
RstD = ExprD
// Note the evaluattion order before this line is important, and will not be changed crossing any JS implementation
Method.call(RstA,RstB,RstC,RstD)

You can feed any number of arguments to any functions as you like, and they only care about just the amount they required
Which means it.replace(a,b,c,d,e) has nothing different with it.replace(a,b) in the view of replace method

PS. Actually there is a limit of arguments number depends on the implementation. Like if you feed too much to a function in the latest Chrome, you will get SyntaxError: Too many arguments in function call (only 65535 allowed)