Method to compare if some periods define by start_date and end_date are mixed

mix_periods.rb

  def mix_periods
    list_period = seasons.inject([]) do |acc, season|
      season.periods.inject(acc) do |a,period|
        a << (period.start_date..period.end_date); a
      end
    end 

    until list_period.empty?
      period_test = list_period.pop
      if list_period.any?{|lp| period_test.cover?(lp.begin) || lp.cover?(period_test.begin) }
        errors.add(:seasons, :period_mix)
        return
      end
    end
  end

mix_periods_spec.rb

    it 'should valid with one season and period not mix' do
      renter_base.seasons = []
      renter_base.seasons << Fabricate.build(:season,
                                             :periods => [
        Fabricate.build(:period, :start_date => 10.day.ago, :end_date => 1.day.ago),
        Fabricate.build(:period, :start_date => 20.day.ago, :end_date => 11.day.ago)
      ])  
      renter_base.should be_valid
    end 

    it 'should_not valid with one season and period mix' do
      renter_base.seasons = []
      renter_base.seasons << Fabricate.build(:season,
                                             :periods => [
        Fabricate.build(:period, :start_date => 10.day.ago, :end_date => 1.day.ago),
        Fabricate.build(:period, :start_date => 20.day.ago, :end_date => 9.day.ago)
      ])  
      renter_base.should_not be_valid
    end 

    it 'should valid with several season and period not mix' do
      renter_base.seasons = []
      renter_base.seasons << Fabricate.build(:season,
                                             :periods => [
        Fabricate.build(:period, :start_date => 10.day.ago, :end_date => 1.day.ago),
        Fabricate.build(:period, :start_date => 20.day.ago, :end_date => 11.day.ago)
      ])
      renter_base.seasons << Fabricate.build(:season,
                                             :periods => [
        Fabricate.build(:period, :start_date => 30.day.ago, :end_date => 21.day.ago),
        Fabricate.build(:period, :start_date => 40.day.ago, :end_date => 31.day.ago)
      ])
      renter_base.should be_valid
    end

    it 'should_not valid with several season and period mix' do
      renter_base.seasons = []
      renter_base.seasons << Fabricate.build(:season,
                                             :periods => [
        Fabricate.build(:period, :start_date => 10.day.ago, :end_date => 1.day.ago),
        Fabricate.build(:period, :start_date => 20.day.ago, :end_date => 11.day.ago)
      ])
      renter_base.seasons << Fabricate.build(:season,
                                             :periods => [
        Fabricate.build(:period, :start_date => 30.day.ago, :end_date => 19.day.ago),
        Fabricate.build(:period, :start_date => 40.day.ago, :end_date => 31.day.ago)
      ])
      renter_base.should_not be_valid
    end