Good point. Fixed.

Replacing Test.expect with Test.assert_equals would be very very useful.

Hi! Nice Kata. If I may suggest something, I would add more detailed explanation what is your understanding of a valid email. As you said, the point is to learn programming language rather than implementing RFC. I think, most people will use regexp. so tuning in the requirements a little big will make them write their own regexps rather than reusing the ones found on the internet.

As an example, you may assume, that valid email should adjoining dots in the domain part. Or the domain should consist of maximum 5 parts (max 4 not adjoining dots). Etc. I think this will make people think and therefore promote this Kata to higher rank.

Good job!