Instead of using null in Math.min.apply(null, numbers), use Math like so: Math.min.apply(Math, numbers). This allows the apply function to use the Math scope (whenever it needs to). Just a best practice bonus, other than that very clean code!

splice is incorrect. Because splice will mutate numbers

You should keep trying, I was about to quit cause thought the tests were wrong but it was my code.

See my post. I agree: totally an issue with the tests.

The random tests are incorrect. All of them. The first argument passed to the deleteNth function should be an array and the second argument should be a number. I actually cannot find a single random test that is passing the correct arguments.

Example:
Testing for delete_nth([17, 33, 1, 47, 33, 47, 17, 33, 17, 17, 17, 47, 47, 13, 17, 33,2)

There should be a second bracket following the (last) 32.

ALSO:

The tests run delete_nth and not deleteNth!