anchor.diff:  
   library engine.incremental_resolver_test;
   
  +import 'package:analyzer/src/context/cache.dart' as task;
   import 'package:analyzer/src/generated/ast.dart';
   import 'package:analyzer/src/generated/element.dart';
   import 'package:analyzer/src/generated/engine.dart';
  
positive.code:     int updateOffset = edit.offset;
      int updateEndOld = updateOffset + edit.length;
      int updateOldNew = updateOffset + edit.replacement.length;
      IncrementalResolver resolver = new IncrementalResolver(
          (analysisContext2 as AnalysisContextImpl)
              .getReadableSourceEntryOrNull(source), null, null, unit.element,
          updateOffset, updateEndOld, updateOldNew);
      bool success = resolver.resolve(newNode);
      expect(success, isTrue);
      List<AnalysisError> newErrors = analysisContext.computeErrors(source);
  
negative.code: 
    @override
    void reset() {
      if (AnalysisEngine.instance.useTaskModel) {
        analysisContext2 = AnalysisContextFactory.contextWithCore();
      } else {
        analysisContext2 = AnalysisContextFactory.oldContextWithCore();
      }
    }
  
    @override
    void resetWithOptions(AnalysisOptions options) {
      if (AnalysisEngine.instance.useTaskModel) {
        analysisContext2 =
                  AnalysisContextFactory.contextWithCoreAndOptions(options);
      } else {
        analysisContext2 =
            AnalysisContextFactory.oldContextWithCoreAndOptions(options);
      }
    }
  
    void setUp() {
  