anchor.diff:    /// Listens to events happening in the script run. See [Once].
     Future once(dynamic eventNameOrTest) {
       if (eventNameOrTest is! String && eventNameOrTest is! EventTest) {
  -      throw new ArgumentError.value(eventNameOrTest, "eventAliasOrTest",
  +      throw new ArgumentError.value(eventNameOrTest, "eventNameOrTest",
             "Must be a String or EventTest, was ${eventNameOrTest.runtimeType}");
       }
   
  
positive.code:     run = new Run._(cpt);
      runModules = new RunModules(script.modules, run, persistence);
  
      script.block(run, runModules.modules);
    }
  
    uis.forEach((createUi) => createUi(runModules.interfaces));
  }
  
  class Script {
  
negative.code:     run = new Run._(ff.getCurrentPlayTime);
      runModules = new RunModules(script.modules, run, persistence);
  
      uis.forEach((createUi) => createUi(runModules.interfaces));
  
      ff.run((ff) {
        script.block(run, runModules.modules);
        persistence.savedEvents.forEach((e) {
          new Future.delayed(e.offset, () {
            runModules.interfaceHandlers[e.moduleName].handle(e.action, e.args);
          });
        });
        ff.fastForward(persistence.savedEvents.last.offset);
  