public MarbleSpec(MarbleTestScheduler scheduler, IReadOnlyDictionary <string, string> marblesLookup)
 {
     _scheduler     = scheduler;
     _marblesLookup = marblesLookup;
 }
 public MarbleSpec(MarbleTestScheduler scheduler, string spec, object?values = null) : this(scheduler, MarbleSpecParser.Parse(spec))
 {
     _values = values;
 }