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: part 'src/core/persistence.dart';
  
  /// Creates a new [Run] for this script by instantiating the modules it
  /// requires, replaying back any saved events provided in [persistence], and
  /// creating and attaching the provided [uis]. Then, calls into that script's
  /// [Block].
  start(Script script,
      {List<CreateUi> uis: const [],
      Persistence persistence: const NoopPersistance()}) {
  
negative.code:     run = new Run._(cpt);
      runModules = new RunModules(script.modules, run, persistence);
  
      uis.forEach((createUi) => createUi(runModules.interfaces));
  
      script.block(run, runModules.modules);
    }
  }
  
  class Script {
  