anchor.diff:      final mockTargets = <_MockTarget>{};
   
       final possiblyAnnotatedElements = [
  -      ...entryLib.exports,
  -      ...entryLib.imports,
  +      ...entryLib.libraryExports,
  +      ...entryLib.libraryImports,
         ...entryLib.topLevelElements,
       ];
   
  
positive.code:       for (final mixin in mockTarget.mixins) {
          cBuilder.mixins.add(TypeReference((b) {
            b
              ..symbol = mixin.name
              ..url = _typeImport(mixin.element)
              ..types.addAll(mixin.typeArguments.map(_typeReference));
          }));
  
negative.code: 
    /// Returns a [Reference] to [symbol] with [url].
    ///
    /// This function overrides `code_builder.refer` so as to ensure that [url] is
    /// given.
    static Reference referImported(String symbol, String? url) =>
        Reference(symbol, url);
  