The tests are fine in javascript, it's your code that's returning the wrong answer:

expected '8 -1' to equal '42 -9' <- expected answer
            ^
        your answer

Not a kata issue.

Which programming language? And what was the exact output of the failed test case?

I highly doubt there is an issue though, unless this is a very recently added translation. Since this kata has thousands of completions.

the tests do not work correctly. they do not return the highest and lowest. like in this case: [
'8', '3', '-5', '42',
'-1', '0', '0', '-9',
'4', '7', '4', '-4'
], it expected '8 -1'.