The entire block in question is an implementation detail of service_named and, as such, is unit tested with the method as a whole already.  It could be split out into a separate method  that would (in all likelihood) be private (and therefore would STILL be most appropriate to unit test as part of the public interface).  The only advantage would be for the express purpose of using that particular idiomatic form, but I don't really see the advantage of doing it just for that.

However, it is odd that "SoftLayer_Account" and "softlayer_account" would lead to the creation of different Service objects.  That should be fixed.