Would you be able to provide test cases?
Thank you for the fun Kata!
I agree with tom-lord 100%. I know you said not to overcomplicate it but for 5kyu it should be more thorough. More examples of why the test are too easy is would be the following.
firstname.lastname@example.org = valid
test..email@example.com = invalid
test."email".firstname.lastname@example.org = valid
test"email"email@example.com = invalid
yet like tom-lord explained
"testemail"@email.com = valid
you could even use an email address with an IP address for the domain part.
firstname.lastname@example.org = valid
testemail@[IPv6:2001:db8::1] = valid
I know the last part is rare but it still is an email address.