public void CanAddAndFind()
        {
            var rangeSet = new RangeSet <int>(0);

            for (var i = 10; i <= 1000; i += 10)
            {
                rangeSet.Add(i, i);
            }

            for (var i = 0; i < 1000; i += 3)
            {
                int n;
                var r = rangeSet.TryFind(i, out n);

                Assert.That(r, Is.True);
                Assert.That(n, Is.EqualTo(i + 10 - i % 10.0).Or.EqualTo(i - i % 10.0));
            }
        }