public static IEnumerable<object[]> Add_TimeSpan_TestData()
{
yield return new object[] { new DateTime(1000), new TimeSpan(10), new DateTime(1010) };
yield return new object[] { new DateTime(1000), TimeSpan.Zero, new DateTime(1000) };
yield return new object[] { new DateTime(1000), new TimeSpan(-10), new DateTime(990) };
}