public void has_existing_entity()
        {
            var newIndex = new EntityIndex <ITestSecondPool, string>(Group, (e, c) => {
                var nameAge = c as NameTestComponent;
                return(nameAge != null
                        ? nameAge.Name
                        : e.Get <NameTestComponent>().Name);
            });

            Assert.IsTrue(newIndex.HasEntities(Key));
            Assert.AreEqual(2, newIndex.GetEntities(Key).Count);
        }