How do I test if an ActiveRecord attribute is an Enum?

ActiveRecord::Enum adds a defined_enums class attribute to the model - a hash storing the defined enums:

MyModel.defined_enums
#=> {"status"=>{"in_progress"=>0, "accepted"=>1, "approved"=>2, "declined"=>3, "closed"=>4, "cancelled"=>5, "submitted"=>6}}

To test if an attribute is an enum you could use:

MyModel.defined_enums.has_key?('status')
#=> true

Unfortunately, defined_enums is not documented.