Print the input.

Yes.

it's usually pretty useful for katas with tests that don't describe themselves to include a line in the beginning of your method that prints the input

I got same problem on same test case, after print out x and y.
x = 'abc', y = 'ac', instead of accept 'a' or 'c',

Result:
Expected: ac, instead got: c

is this correct?

you can write:

console.log(x);
console.log(y);

at the beginning of your function,then you can see the parameters when you run test cases