It's not a reversed number, it's a number with its digits rearranged.

Maybe 1210 instead of 1021, send the 0s to the end perhaps. If I understood correctly, the reversed number should be the largest possible...?

/

The output should be int.

Anyone who has solved the kata can see your code if you post in discourse. This kata is almost 8 years old and has over 64k solves in javascript. The chance that someone will find a bug in the kata at this point is extremely small (but not impossible, I guess). In this case, it's pretty simple to look at the test cases and see what the test actually expects your function to return.

No, it's the other way around, and you can convert one into the other, why do you say you can't?

there are problems with test#4 and test#5
2110 cannot be converted into 1021
and 987654321 into 123495678

@Test
public void test_04() {
    assertEquals(2110, DescendingOrder.sortDesc(1021));
}

@Test
public void test_05() {
    assertEquals(987654321, DescendingOrder.sortDesc(123495678));
}