anchor.diff:      return source;
     }
   }
  +
  +class _CompilationUnitElementMock extends TypedMock
  +    implements CompilationUnitElement {}
  
positive.code:     index.indexDeclarations(testUnit);
    }
  
    test_indexUnit_nullUnit() async {
      index.indexUnit(null);
    }
  
negative.code: import 'package:analyzer/src/generated/source.dart';
  import 'package:analyzer/src/summary/idl.dart';
  import 'package:test_reflective_loader/test_reflective_loader.dart';
  import 'package:typed_mock/typed_mock.dart';
  import 'package:unittest/unittest.dart';
  
  import '../../abstract_single_unit.dart';
  