Ginkgo - skip tests that don't match an expression

Question

Trying to write a REGEX for the ginkgo --skip flag, that would skip tests that do NOT contain a string ("test1"). AFAIK golang doesn't support '!' (this post)

I know I can use --focus, but prefer --skip for reasons.

How do I go about creating a negative match expression for this purpose?

I tried using (?i)^(?!.*test1).* but this expression doesn't work, as the "!" is treated literally and is not supported in golang.