0112 is the same as 112

Yes. Which is why, you will never receive 0112 as input. That's why it didn't happen.
That is convincing, right? We can rule that out.
myfunction(0112) <-- myfunction is going to receive 112, it will not be able to see "0112" in any shape or form

And if that is ruled out, then, you found 0112 somewhere else.

Additionally, looking at the test code, there is no such case. But the above is sufficient to already know that's not what happened.

So it comes down to re-measuring, because the measurement of 0112 can't be. And yeah you might not successfully do this but ... that's okay.
Typically what you can do to measure input is to print it out as the first thing you do in your function. For example:

func descendingOrder(of number: Int) -> Int {
  print(number)
  return number
}

Ideally you'd also figure out how you mistakenly found 0112, just because it's good to understand what went wrong.

If on the other hand the tests were based on strings and "0112" was generated, then you would still be receiving 112 and 2110 would have been expected. The test case would be 112 -> 2110. Yes that would be wrong, but that is also not happening and it wouldn't be 0112 -> 2110 which cannot be. It is however plausible that your code does this, that your code creates that string, converts it to int, loses the zero. That'd be something you created and that would mean you're measuring not the input but some intermediary state in your own solution.

There is no test with that input in javascript and the expected order is descending, so, no idea what you're talking about.

This test DOES exist. JS treats numbers with leading 0 as octal. After researching a bit I have learnt that it would be a bad practice anyway to use numbers with leading 0 in real life code, therefore I would suggest not to waste time to search for a workaround, but rather to remove this example from tests.

It's not that it doesn't matter, it's that it isn't different. It's the same value. The difference would only exist in a string, so when you talk about 0112, you're talking about strings. But you're not receiving a string so this isn't what happened.

Find out what value you did receive. It's not 112, that's something you more or less made up.

So one test doesn't work: 0112 -> 2110

That test does not exist. It cannot exist. However you came up with that, you mis-measured.
Re-measure.

I don't know swift but I'm pretty sure 0112 is not a separate value from 112, you're thinking of strings.
I'm guessing you have not actually made a measurement showing you that input was 112? So it's a guess? Measure.