Simply returns DateTime.Now or DateTime.UtcNow
상속: ITimeSource
 public void UtcNow_should_return_within_100_milliseconds_of_DateTimeNow()
 {
     ITimeSource uut = new DateTimeNowTimeSource();
     Math.Abs((uut.UtcNow - DateTime.UtcNow).TotalMilliseconds).Should().BeLessThan(100);
 }
 public void UtcNow_should_return_within_100_milliseconds_of_DateTimeNow()
 {
     var uut = new DateTimeNowTimeSource();
     uut.UtcNow.Should().BeWithin(100.Milliseconds()).Before(DateTime.UtcNow);
 }