describe :queue_num_waiting, shared: true do
  it "reports the number of threads waiting on the queue" do
    q = @object.call
    threads = []

    5.times do |i|
      q.num_waiting.should == i
      t = Thread.new { q.deq }
      Thread.pass until q.num_waiting == i+1
      threads << t
    end

    threads.each { q.enq Object.new }
    threads.each {|t| t.join }
  end
end