anchor.diff:  mixin SummaryTestCases implements SummaryBlackBoxTestStrategy {
     /// Get access to the linked defining compilation unit.
     LinkedUnit get definingUnit => linked.units[0];
  +
  +  FeatureSet get enableNnbd =>
  +      FeatureSet.forTesting(additionalFeatures: [Feature.non_nullable]);
   
     /// TODO(scheglov) rename "Const" to "Expr" everywhere
     void assertUnlinkedConst(UnlinkedExpr constExpr, String sourceRepresentation,
  
positive.code:   }
  
    test_field_static_final_late() {
      featureSet = FeatureSet.forTesting(
          sdkVersion: '2.2.2', additionalFeatures: [Feature.non_nullable]);
      UnlinkedVariable variable =
          serializeClassText('class C { static late final int i = 0; }')
              .fields[0];
  
negative.code:   }
  
    test_variable_late() {
      featureSet = enableNnbd;
      UnlinkedVariable variable =
          serializeVariableText('late int i;', variableName: 'i');
      expect(variable.isLate, isTrue);
  