anchor.diff:      // List<T> <: List<String> can be satisfied
       _checkIsSubtypeMatchOf(
           listType(T), futureOrType(listType(stringType)), [T], ['T <: String'],
  -        covariant: true);
  -  }
  -
  -  void test_variance_covariant() {
  -    // class A<out T>
  -    var tCovariant = typeParameter('T', variance: Variance.covariant);
  -    var tType = typeParameterType(tCovariant);
  -    var A = class_(name: 'A', typeParameters: [tCovariant]);
  -
  -    // A<num>
  -    // A<T>
  -    var aNum = interfaceType(A, typeArguments: [numType]);
  -    var aT = interfaceType(A, typeArguments: [tType]);
  -
  -    _checkIsSubtypeMatchOf(aT, aNum, [tType], ['T <: num'], covariant: true);
  -  }
  -
  -  void test_variance_contravariant() {
  -    // class A<in T>
  -    var tContravariant = typeParameter('T', variance: Variance.contravariant);
  -    var tType = typeParameterType(tContravariant);
  -    var A = class_(name: 'A', typeParameters: [tContravariant]);
  -
  -    // A<num>
  -    // A<T>
  -    var aNum = interfaceType(A, typeArguments: [numType]);
  -    var aT = interfaceType(A, typeArguments: [tType]);
  -
  -    _checkIsSubtypeMatchOf(aT, aNum, [tType], ['num <: T'], covariant: true);
  -  }
  -
  -  void test_variance_invariant() {
  -    // class A<inout T>
  -    var tInvariant = typeParameter('T', variance: Variance.invariant);
  -    var tType = typeParameterType(tInvariant);
  -    var A = class_(name: 'A', typeParameters: [tInvariant]);
  -
  -    // A<num>
  -    // A<T>
  -    var aNum = interfaceType(A, typeArguments: [numType]);
  -    var aT = interfaceType(A, typeArguments: [tType]);
  -
  -    _checkIsSubtypeMatchOf(aT, aNum, [tType], ['T <: num', 'num <: T'],
           covariant: true);
     }
   
  
positive.code:         covariant: true);
    }
  
    void test_x_futureOr_fail_both_branches() {
      // List<T> <: FutureOr<String> can't be satisfied because neither
      // List<T> <: Future<String> nor List<T> <: int can be satisfied
  
negative.code:   }
  }
  
  @reflectiveTest
  class TypeSystemTest extends AbstractTypeSystemTest {
    InterfaceTypeImpl get functionClassTypeNone {
  