Next previous weekday

Some more general usable extensions on DateTime include the ability to get the next or previous DayOfWeek, or get the last or first DayOfWeek of the Month.

Example: Get next tuesday

[Test]
public void get_next_and_last_tuesday() {
    var a_saturday = new DateTime(2011, 8, 20);

    var nextTuesday = a_saturday.NextDayOfWeek(DayOfWeek.Tuesday);
    var lastTuesday = a_saturday.LastDayOfWeek(DayOfWeek.Tuesday);
    Assert.IsTrue((nextTuesday.DayOfWeek == DayOfWeek.Tuesday) && (nextTuesday == new DateTime(2011, 8, 23)));
    Assert.IsTrue((lastTuesday.DayOfWeek == DayOfWeek.Tuesday) && (lastTuesday == new DateTime(2011, 8, 16)));
}  

Example: First and Last Tuesday of August

[Test]
public void get_first_and_last_tuesday_of_august() {
    var a_saturday = new DateTime(2011, 8, 13);

    var firstTuesday = a_saturday.FirstDayOfWeekOfTheMonth(DayOfWeek.Tuesday);
    var lastTuesday = a_saturday.LastDayOfWeekOfTheMonth(DayOfWeek.Tuesday);
    Assert.IsTrue((firstTuesday.DayOfWeek == DayOfWeek.Tuesday) && (firstTuesday == new DateTime(2011, 8, 2)));
    Assert.IsTrue((lastTuesday.DayOfWeek == DayOfWeek.Tuesday) && (lastTuesday == new DateTime(2011, 8, 30)));
}