Yes, the random tests are vulnerable to input modification. No, if you do not modify the input the tests are not wrong. Yes, if you modify the input you deserve whatever you get.

Note that [].sort modifies its input.

Not a kata issue. Closing.

Same error without modifying the input in JS :

[ 19, 72, 16, 50, 25, 92, 80, 23, 40, 63, 26, 99, 42, 18, 68, 3, 75, 96 ]

Expected: '[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18]', instead got: '[15, 6, 17, 9, 13, 3, 4, 14, 11, 8, 12, 1, 10, 16, 7, 18, 5, 2]'

What language is failing? I'll look into why it is doing so now.

do you mutate the input?

What language are you using? I just realized there are not 900 tests in python (just some...). Unfortunately, I won't be capable of helping you in PHP or JS, sorry.

I'd bet that if you fail some tests, with inputs as big as they are, the assertion message will cause the very same problem than if you were actually printing something to the console yourself.