Actually it should be [ 42 ]

Hi. I am thrown by this final test case. Why would this resulting array be ['0']? Is this possibly in error? It looks to be a duplicate value from the test just above.

Array.prototype["3"] = 42;
let filtered_array_lower = new Array(10).filter(x => true);
Test.assertSimilar(Object.keys(filtered_array_lower), ['0'], "Oh no! It was fooled by Array.prototype['3']");

I think this is the least useful kata I've found, because of bizarre formatting issues discussed. I've been going through these to prep for an interview, and I wish I hadn't found this one tbh.