What does including the type in the describe block of a rspec do?

Question

I don't think the type part is necessary, what does it actually do?

RSpec.describe Auction, :type => :model do

Answer 1

The type metadata is necessary to include the correct rspec-rails support functions. There can be different spec types, inclucing controller, view, helper, mailer etc. Look more from here. Model specs are more specifically described here.

Note: RSpec versions before 3.0.0 automatically added metadata to specs based on their location on the filesystem. In RSpec3 this behaviour must be defined separately in configuration:

​# spec/rails_helper.rb
RSpec.configure do |config|
  config.infer_spec_type_from_file_location!
end

Therefore - if you are using RSpec 3, then without the upper configuration you cannot ignore the type declaration when creating specs.

There is also possibility to define your own custom metadata type like this:

​# set `:type` for serializers directory
RSpec.configure do |config|
  config.define_derived_metadata(:file_path => Regexp.new('/spec/serializers/')) do |metadata|
    metadata[:type] = :serializer
  end
end