Why should it? April is in the 2nd quarter.

Don`t work with test case Expect(QuarterOf(4)).To(Equal(1))

good as shortest solution, but not obvious with magic numbers

Ruby 3.0 should be enabled (Refer this & this for more detail)

This is a very simple kata, only uses basic language structures (unless you want to use regex which also just uses basic regex) and the test suite is so long that hard coding it would be harder than the solution. In this case, I don't see the necessity of random cases - however, they are added anyway.

That isn't an issue.

Nice detail.

Great, learned about max method parameter! Thanks for this kata.

The two cases for words ending in "-y" ("days", "buys" vs. "flies") should be clearer expressed in the task statement.

Please add some random tests.

Cheecky solution for the words in the test ending on consonant and 'y'!

You are totally right. I did not read it correctly. My mistake, sorry.

But it is. The instructions say: "...If a singular noun ends with a consonant and '-y', change '-y' to '-ies'. All other words just add '-s'". Isn't that rule enough?

Currently the difference in pluralizing day and fly is not covered in the rules in the instructions.
It would be helpful to add the relevance of vowels to the rules.