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
attr_accessible
attr_protected
If for some reason RSpec is tripping up on juicedM3's answer above like mine was you can do something like this:
specify { expect { Model.new(unaccessible_attr: value) }.to raise_error(ActiveModel::MassAssignmentSecurity::Error) }