Retired due to it being to close a duplicate to the RangeExtraction kata.

Thanks, added one more test as You suggest.

I suggest adding a list which starts with a number other than 1 to the tests. I spotted at least one solution that would be obsolete if this test were included.

I agree with you, but I think that my version has a right to exist

This is almost a complete duplicate of Range Extraction, except that provides an array of numbers, and expects a dash only when there is a contiguous range of 3 or more integers.

Thanks, added one more test, correct description

First:
Missing check for a single last number while saving:
Test.assertEquals(createRangesString('1,2,3,4,5,7,8,9,11'),'1-5, 7-9, 11' );
My first try failed with such string but it let me save even if the algorythm was failing with a single last number.

Second:
in the description you use function named minimiseString(str) but into code function's named createRangesString(str). Just a minor thing but this could be a bit confusing.

Thank you very much for your advice and for correcting my sloppy English)
I agree that it is wrong to allow non-numeric characters and removed it from the tests. I also changed the name of the function a bit, but still left the input and output parameters as strings. I think it will help improve the skills of working with strings.

There are a few minor issues from my perspective:

It's confusing why in the case when there are two numbers next to each other, 17 and 18, why they'd be outputted seperately instead of combined into one range 17-18.

The phrase "Numbers in a string in ascending order" in the description should be "The numbers in the string will always be in ascending order.".

It feels a bit arbitrary to me why you'd have the restriction that the numbers are in ascending order, but then also allow non-number input.

Those minor issues aside, just as a suggestion, this question would be more clear to me if instead of being minimiseString, it was createRanges, which would take an unordered array of numbers, e.g. [1, 3, 2, 5, 4, 9, 8, 7], and returns a sorted array of ranges, e.g. [[1, 5], [7, 9]].