I like when I get a comment on an old solution and I'm like "What the fuck did I write?"

woah

Not a kata issue, but added "keeping their order" to the description.

The order is as the original list, [1,3] isn't the same as [3,1], you can see the order in the last example in the description, if any order would be valid, it would be specified.

tests seem to fail because of diff in order of result arr:

Testing for array_diff([14, -3, -14, 16, -11, 2, 13, 6, -12, 0, 10, -12, -14], [-11, -7, -7, 3, -2, 20, -7, 11, 3, 16, 18, 1, 6, -11, -18, 0, 7, 3])
[14, -3, -14, -14, 2, 13, -12, -12, 10] should equal
[14, -3, -14, 2, 13, -12, 10, -12, -14]

Completed in 0.02ms

There are a few more examples but here it's easiest to see.
There's nothing in the instructions about the result print order, nor does there appear to be any concrete ordering to the test arrays.

would apprecaise the help,
Thanks.

There is no error in the tests.
Please before posting an issue look at the top of the page to see how many people passed the kata (114 with Rust); if there were errors somebody would already have seen them.
Read the description again.