A useful feature for the MockResource testing class would be the ability to specify additional properties and return them when the MockResource is adapted into a ValueMap.
I use this on nearly every project I've been on to test services. I've attached a patch file which adds two methods:
addProperty - add a single key, value set
getProperties - returns the map of properties which can be modified
And then in the adaptTo method I just added all of the properties in the map into the returned ValueMap.