Simple scheme for unit testing cancan abilities

ability_spec.rb

require 'spec_helper'

describe Ability do
  let(:district) { Factory :district }
  let(:root) { Factory :root_user }
  let(:admin) { Factory :admin_user, district: district }
  let(:other_admin_in_district) { Factory :admin_user, district: district }
  let(:admin_in_other_district) { Factory :admin_user }
  let(:contributor) { Factory :contributor_user, district: district }
  let(:contributor_in_other_district) { Factory :contributor_user }

  context "for a root user" do
    subject { Ability.new root }

    it { should be_able_to :index, User }
    it { should be_able_to :manage, root }
    it { should be_able_to :manage, admin }
    it { should be_able_to :manage, contributor_in_other_district }
  end

  context "for an admin user" do
    subject { Ability.new admin }

    it { should be_able_to :index, User }
    it { should be_able_to :admin, contributor }
    it { should be_able_to :admin, other_admin_in_district }
    it { should_not be_able_to :admin, contributor_in_other_district }
    it { should_not be_able_to :admin, admin_in_other_district }
    it { should_not be_able_to :admin, root }
  end

  context "for a contributor" do
    subject { Ability.new contributor }

    it { should_not be_able_to :index, User }
    it { should_not be_able_to :admin, contributor }
    it { should_not be_able_to :admin, admin }
    it { should_not be_able_to :admin, root }
  end
end

can_can_matchers.rb

module CanCanMatchers
  def be_able_to(permission, object)
    BeAbleToMatcher.new :be_able_to, permission, object
  end

  class BeAbleToMatcher
    attr_reader :permission
    attr_reader :object
    attr_reader :subject

    def initialize(macro, permission, object)
      @macro = macro
      @permission = permission
      @object = object
    end

    def matches?(subject)
      @subject = subject
      @subject.can? permission, object
    end

    def description
      "be able to #{permission} #{object}"
    end

    def negative_failure_message
      "Did not expect that #{subject} can? #{permission} #{object}"
    end

    def failure_message
      "Expected that #{subject} can? #{permission} #{object}"
    end
  end
end

module RSpec::Matchers
  include CanCanMatchers
end

Thanks for that! I have a pretty simple permission scheme right now, so I've just been testing abilities in the User spec, but I think as it grows, I'll need to move them to a separate file.

I made a similar template for unit testing models a few years back that was incredibly polarizing. Feel free to check it out and offer feedback if you'd like: https://gist.github.com/kyletcarlson/6234923