So we have been setting up attr_accessible and attr_protected on many fields through out our Rails 3.2 app. For now we really don\'t test to ensure
I was looking for something similar and then I was told about the shoulda-matcher allow_mass_assigment_of. That ended up working for me without creating a custom matcher.
it { should allow_mass_assignment_of :some_field }
it { should_not allow_mass_assignment_of :field_name }
Hope this helps someone else.