I have got same trouble, althouth tryed three solutions, based on Queue, HashSet and dumb sorting array in-place. All solutions begins with check for empty or odd array.

Minor description issue:

get_honor('jhoffner')

For bishop1 = "d8" and bishop2 = "b5", the output should be ["b5", "d8"].

I can't understand why they should swap?

Minor issue in description: If t --> he pair is of the same color

A very interesting problem, I'd like to solve it, but preferably in C#.

No, it's not a problem really (at least in this simple task) and it is not banned in C#, of course. I just don't like such way because it's bad practice, IMHO. Never mind, I'm just a stickler and a perfectionist. :)

This is a very strange way to overcome such trouble, IMHO. Why not use long or BigInteger?

Why C# code obliged to return double?

public string[] NewNumeralSystem(string number){

System.ArgumentOutOfRangeException : Index was out of range. Must be non-negative and less than the size of the collection.
Parameter name: index

There is a error somewhere in random tests...

Parameter of C# function must be char, not string.

C# function named GetEvenNumber instead of IsVeryEvenNumber, expected by unit tests.

I can't understand why you may need to modify the array or clone it. I think You'd better reconsider your solution.

I could not understand why I can't write such a trivial program. After analyzing many tests I realized that the description is inaccurate. In this sentence should be the word "letters": "last letter of the first argument (body) - otherwise the tail wouldn't fit!"