public void CurrentStartOfMonthShouldReturnExpectedResult() { using ( ShimsContext.Create() ) { ShimDateTime.TodayGet = () => new DateTime( 2013, 6, 15 ); var expected = new DateTime( 2013, 6, 1 ); var target = new GregorianCalendar(); var actual = target.CurrentStartOfMonth(); Assert.Equal( expected, actual ); } }