abilities_matcher.rb

# RSpec CanCan matcher.
#
# When testing your user must have an id otherwise a nil foreign key will
# match on new records.
#
# Examples
#
#   describe User do
#     subject { User.create! }
#
#     it { should     have_ability(:read).for(Post.new) }
#     it { should_not have_ability(:edit, :update, :destroy).for(Post.new) }
#   end
#
RSpec::Matchers.define :have_ability do |*actions|
  match_for_should do |user|
    check_subject!
    actual_abilities(actions, user) == expected_abilities(actions, user, true)
  end

  match_for_should_not do |user|
    check_subject!
    actual_abilities(actions, user) == expected_abilities(actions, user, false)
  end

  chain :for do |target|
    @target = target
  end

  failure_message_for_should do |user|
    "expected: #{expected_abilities(actions, user, true)} for #{user} on #{@target.inspect}\n     got: #{actual_abilities(actions, user)}"
  end

  failure_message_for_should_not do |user|
    "expected: #{expected_abilities(actions, user, false)} for #{user} on #{@target.inspect}\n     got: #{actual_abilities(actions, user)}"
  end

  def actual_abilities(actions, user)
    @actual_abilities ||= begin
      ability = Ability.new(user)

      actions.reduce({}) do |results, action|
        results.merge({ action => ability.can?(action, @target) })
      end
    end
  end

  def expected_abilities(actions, user, expectation)
    actions.reduce({}) do |abilities, action|
      abilities.merge({ action => expectation })
    end
  end

  def check_subject!
    raise "Ability subject is nil! Subject should be defined: `have_ability(...).for(subject)`" if @target.nil?
  end
end