public static void AdvanceBy(this TestScheduler @this, TimeSpan time)
 {
     @this.AdvanceBy(time.Ticks);
 }
 public static void AdvanceMinimal(this TestScheduler @this) =>
 // not technically minimal, but advancing by a single tick doesn't always work as expected (a bug in Rx?)
 @this.AdvanceBy(TimeSpan.FromMilliseconds(1));