loop through each instance, wait for a new one to come up, then deregister and terminate the old one

spec/support/fake_auto_scaling.rb

@@ -42,6 +42,10 @@ module AWS
           self.instance_variable_set "@#{key}", value
         end
       end
+
+      def ec2_instances
+        []
+      end
     end
   end
 end

spec/support/fake_elb.rb

@@ -12,10 +12,20 @@ module AWS
       end
     end
 
-    class InstanceCollection
+    class InstanceCollection < Array
       def initialize
       end
 
+      def register(*instances)
+        self.concat instances
+      end
+
+      def deregister(*instances)
+        instances.each do |i|
+          self.delete i
+        end
+      end
+
       def health
         @health ||= [
           {