Less optimal with larger numbers, but a very clean solution.

This does not enforce the requirement that s is built from characters drawn from part1 or part2, in the order in which they occur. 's' must be found AFTER 'r'!

I just looked through the C# translation, I assume you're speaking about the randomness of the result?

The actual indata looks random to me, but the result could be easy to guess.

I have rejected it. The SadPath2 is correct as it is. The order of the characters is relevant.

That being said, I appreciate that you spent the time to improve the kata.

I welcome help with the different languages. Most of the translations are written and approved by other people. :-)

The "random tests" in C# are not random at all.

You are misunderstanding the task, your proposed changes in tests and solution are completely wrong. Unpublish your fork, otherwise a moderator should reject it (the author's been active recently).

This test is wrong in the C# fork:
public void SadPath2()
{
Assert.IsFalse(StringMerger.isMerge("codewars", "code", "wasr"), "codewars can't be created from code and wasr");
}

I have updated the test and code to fully run with the correct test. Needs approving

This test is wrong in the C# fork:
public void SadPath2()
{
Assert.IsFalse(StringMerger.isMerge("codewars", "code", "wasr"), "codewars can't be created from code and wasr");
}

Updated the test and code to fully run with the correct test. Needs approving

well done.