public void CacheIsLocalToSubclass() { StringWriter sw = new StringWriter(); FormatterOne f1 = new FormatterOne(); FormatterTwo f2 = new FormatterTwo(); DateTime dt1 = DateTime.Today.AddMinutes(10); f1.FormatDate(dt1, sw); f2.FormatDate(dt1, sw); Assert.AreEqual(2, FormatterOne.invocations); }