DNA to RNA doesn't only translate T to U—the Science here is incorrect. It goes:

C <-> G /
T -> A /
A -> U

When you solve a kata, the "test" button becomes "submit" in the code editor. As long as you hit that, your solution is posted to the solutions page (except in a few buggy cases).

how to post in solutions

There is no need to post solutions in discourse, that's what the solutions page is for. Also, when posting possible spoilers, please use the spoiler flag (I've added the spoiler flag to your post).

ooooooo! I'm so happy. It's the second Kata i solved by myself.

What do you mean? It's just replacing the character T with the character U.

Enabled in this fork

Well the assertion messages of Python test framework are suboptimal.

the issue here is probably not about whether their solution is correct, but that the test output itself can (if misreading, but reasonably so) seem to contradict the instructions (as it may seem to claim that 'TTTTUUUUU' was the input)

..which I agree with. this is poor wording which assumes a different context for the solver than the solver is actually in

Your algorithm is not correct. You append an 'U' for every 'T' (not exactly, actually it's even weirder but you get the point).

Not a kata issue.

"'TTTTUUUUU' should equal 'UUUU'
'GCATUU' should equal 'GCAU'"

Say what now? I thought this was supposed to be just about converting Ts to Us. What is this?

Please do not post your solutions in kata discourses. It's not necessary, and they are spoilers.