anchor.diff:  
       // update .dart_tool/package_config.json
       callbacks.now++;
  -    resourceProvider.modifyFile(
  +    modifyFile(
         packageConfigPath,
         (PackageConfigFileBuilder()..add(name: 'my', rootPath: '../'))
             .toContent(toUriStr: toUriStr),
  
positive.code:     expect(callbacks.currentContextRoots, contains(examplePath));
      var exampleSources = callbacks.currentFileSources(examplePath);
      expect(exampleSources, hasLength(1));
      expect(exampleSources.first.uri.toString(),
          (Uri.file('$examplePath/example.dart').toString()));
    }
  
    void test_setRoots_addFolderWithoutPubspec() {
  
negative.code:     expect(callbacks.currentContextRoots, contains(projPath));
      var projSources = callbacks.currentFileSources(projPath);
      expect(projSources, hasLength(1));
      expect(projSources.first.uri, toUri('$libPath/main.dart'));
  
      expect(callbacks.currentContextRoots, contains(examplePath));
      var exampleSources = callbacks.currentFileSources(examplePath);
      expect(exampleSources, hasLength(1));
      expect(exampleSources.first.uri, toUri('$examplePath/example.dart'));
    }
  
    void test_setRoots_addFolderWithNestedPubspec() {
  