public void TestDemoDateTimeProvider()
        {
            var utcNow = DateTime.UtcNow;

            //Act
            var provider1   = new DateTimeProvider(utcNow);
            var iso8601_1st = provider1.GetIso8601Format();
            var provider2   = new DateTimeProvider(iso8601_1st);
            var iso8601_2nd = provider2.GetIso8601Format();

            //Assert
            Assert.Equal(utcNow, provider1.GetStoredDateTime(), TimeSpan.FromSeconds(0.001));
            Assert.Equal(utcNow, provider2.GetStoredDateTime(), TimeSpan.FromSeconds(0.001));
            Assert.Equal(iso8601_1st, iso8601_2nd);
        }