TL;DR (sorry 4 the yapping): bad title and really weak tests (maybe consider a proper "Issue" tag for tests).

About tags:

• I would consider adding the "ASCII Art" tag.

About tests:

• Definitely add heavier and/or more random tests. Also, make sure the tests cover odd sizes, as currently, there's only one test with an odd size (5).

About the kata itself:

• Personally I would add sizes from 0 to 4, I know they don't exactly form a "wave effect matrix" but they can be easily generated. However, there's nothing wrong by keeping the "size >= 5" constraint.
• Lastly, I'm not a big fan of the title but I would at least add a space before the parentheses start.

Really nice yet simple kata, hope you update it :D
It's a simple kata that perfectly fits the 6 kyu range, hope I see it approved soon. 👍

Fun kata, my solution is kinda sloppy but hehe.

thx, is my firts Kata, lets see how it goes

Use of the word "spiral" is unhelpful