Current week...

blueprints.rb

Timecop.freeze(Time.local(2011, 11, 8, 12, 0, 0))
start  = Time.now - 2.days
finish = Time.now + 5.days

LeadAssignmentPeriod.blueprint do
  start_date { start }
  end_date   { finish }
end

lead_assignment_period_spec.rb

require 'spec_helper'

describe LeadAssignmentPeriod do
  context 'scopes' do
    context '.current' do
      context 'when there is a period for the current week' do
        before { LeadAssignmentPeriod.make!(:totaling_to_100) }
        subject { LeadAssignmentPeriod.current }

        it { should have(1).lead_assignment_period }
      end
    end
  end
end

scope.rb

scope :current, lambda {
  now = Time.now
  where('start_date <= ?', now).
  where('end_date >= ?', now)
}