have_index_for doesn't seem to work

[zedtux]

I'm using Mongoid 5.1.6 in a Rails 4.2.2 application.

I'm able to test all the Mongoid things of my models excepted the indexes.

I have a model like this:

class ConversationUnreadMessage
  include Mongoid::Document
  include Mongoid::Timestamps::Short
  include MongoSerializer

  # ~~~~ Fields ~~~~
  field :o, as: :operator_id, type: Integer
  field :c, as: :conversation_id, type: String
  field :m, as: :conversation_message_id, type: String

  # ~~~~ Index ~~~~
  index({ operator_id: 1, conversation_id: 1 }, background: true)
end

And my spec file like this:

require 'rails_helper'

RSpec.describe ConversationUnreadMessage, type: :model do
  describe 'Fields' do
    it { is_expected.to have_field(:o).with_alias(:operator_id).of_type(Integer) }
    it { is_expected.to have_field(:c).with_alias(:conversation_id).of_type(String) }
    it { is_expected.to have_field(:m).with_alias(:conversation_message_id).of_type(String) }
  end

  describe 'Indexes' do
    it { is_expected.to have_index_for(operator_id: 1, conversation_id: 1).with_options(background: true) }
  end
end

The tests are failing with the following:

Failures:

  1) ConversationUnreadMessage Indexes should have an index for {:operator_id=>1, :conversation_id=>1} with options of {:background=>true}
     Failure/Error: it { is_expected.to have_index_for(operator_id: 1, conversation_id: 1).with_options(background: true) }
       Expected ConversationUnreadMessage to have an index for {:operator_id=>1, :conversation_id=>1} with options of {:background=>true}, got no index for {:operator_id=>1, :conversation_id=>1}
      ...

I did it following this gem's README.md file instructions.

Is there anything else that shall be done in order to get this to work? Or should it be a bug of this gem?

[dblock]

Looks like a bug, appreciate a PR with a fix.

[zedtux]

OK thank you @dblock for your comment.