public void IndexAtLoopedTest()
        {
            var people = RandomData.GeneratePersonRefCollection <PersonProper>(10);

            System.Collections.ObjectModel.Collection <PersonProper> nullPeople = null;

            var result = people.IndexAtLooped(5);

            Assert.IsNotNull(result);

            Assert.ThrowsException <ArgumentNullException>(() => nullPeople.IndexAtLooped(5));
        }