This spec is great, but it's actually already implemented in https://github.com/jruby/jruby/blob/master/spec/ruby/core/hash/to_a_spec.rb.

The reason it's not where you looked for it is that RubySpec distinguishes between the language and the core. The separation isn't always perfect though - and `for` is a good example of that as it usually just calls core methods for you.

Also, even if this was needed, we don't modify RubySpec within the JRuby repository - instead we make changes in their repository and then pull them in every now and again.

So although writing tests and specs when you write code is usually a good idea, I can't merge this modification in.