Implement Sidekiq::Stats.size

Useful for other libraries, like hirefire.
Implemented specifically to clean up a6de8329.
Will close #386 when merged.

lib/sidekiq/stats.rb

@@ -22,5 +22,14 @@ module Sidekiq
     def backlog
       queues_with_sizes.map {|_, size| size }.inject(0) {|memo, val| memo + val }
     end
+
+    def size(*queues)
+      return backlog if queues.empty?
+      queues.
+        map(&:to_s).
+        inject(0) { |memo, queue|
+          memo += Sidekiq.redis { |conn| conn.llen("queue:#{queue}") }
+        }
+    end
   end
 end

test/test_stats.rb

@@ -76,16 +76,27 @@ class TestStats < MiniTest::Unit::TestCase
           conn.sadd 'queues', 'bar'
         end
       end
+
       describe "queues_with_counts" do
         it "returns queue names and corresponding job counts" do
           assert_equal [["foo", 1], ["bar", 2]], Sidekiq::Stats.queues_with_sizes
         end
       end
+
       describe "backlog" do
         it "returns count of all jobs yet to be processed" do
           assert_equal 3, Sidekiq::Stats.backlog
         end
       end
+
+      describe "size" do
+        it "returns size of queues" do
+          assert_equal 1, Sidekiq::Stats.size(:foo)
+          assert_equal 1, Sidekiq::Stats.size("foo")
+          assert_equal 3, Sidekiq::Stats.size("foo", "bar")
+          assert_equal 3, Sidekiq::Stats.size
+        end
+      end
     end
 
   end