public void ExpiryEndOfYearTests() { var endOfYearList = new List <DateTime>(); var current = new DateTime(2019, 1, 1); var end = new DateTime(2020, 1, 1); while (current < end) { var endOfYear = Expiry.EndOfYear(current); endOfYearList.Add(endOfYear); Assert.AreEqual(1, endOfYear.Day); Assert.AreEqual(end.Year, endOfYear.Year); Assert.Greater(endOfYear, current); current = current.AddDays(1); } var actual = endOfYearList.Distinct().Count(); Assert.AreEqual(1, actual); }