Description should specify which of multiple possible longest repeatings substrings should be chosen ( which should then be tested ).

If any will do, this should still be specified. Note that it is very possible to allow ( and test ) returning any longest repeating substring.

No sample tests and horrible error feedback in Ruby

BF Translation

This was more challening than I thought at first.

One thing I don't understand: Why does the original array have to be shallow copied to preserve the order of items that have equal last characters?

As already stated below, this is a clear duplicate of:
http://www.codewars.com/kata/find-the-2nd-largest-integer-in-array

The minor difference of smallest/largest does not make it unique or novel.

• tidy up the description (at least use code blocks for code)
• add sample tests from description:

Test.assert_equals(find_2nd_smallest([1,2,3]), 2)
Test.assert_equals(find_2nd_smallest([1,1,1,1,1]), nil)
Test.assert_equals(find_2nd_smallest([1,'a','2',3,3,4,5,'b']), 3)

Thanks, @nakulgupta18! Nice kata, but sometimes letter 'y' is vowel. It would be great, if you will update your kata algo & test cases.

In C#, there are only seven fixed tests. Needs random tests.

In C#, the expected and actual fields for tests are backwards.

Additionally, the method name greet should be Greet, as public method names are PascalCased in C#.