anchor.diff:  import "package:testing/testing.dart"
       show Chain, ChainContext, Result, Step, TestDescription, runMe;
   
  -import "package:yaml/yaml.dart" show YamlMap, loadYamlNode;
  +import "package:yaml/yaml.dart" show YamlList, YamlMap, loadYamlNode;
   
   import "incremental_utils.dart" as util;
   
  
positive.code:   }
  }
  
  Future<Null> basicTest(Map<String, String> sourceFiles, String entryPoint,
      bool strong, List<String> invalidate, Directory outDir) async {
    Uri entryPointUri = outDir.uri.resolve(entryPoint);
    Set<String> invalidateFilenames = invalidate?.toSet() ?? new Set<String>();
    List<Uri> invalidateUris = <Uri>[];
    Uri packagesUri;
    for (String filename in sourceFiles.keys) {
  
negative.code:   Map<String, String> sourceFiles;
    CompilerOptions options;
    TestIncrementalCompiler compiler;
    for (YamlMap world in worlds) {
      bool brandNewWorld = true;
      if (world["worldType"] == "updated") {
        brandNewWorld = false;
  