anchor.diff:  }
   
   @reflectiveTest
  -class IsNonNullableTest extends _NullableBase {
  +class IsNonNullableTest extends AbstractTypeSystemNullSafetyTest {
     void isNonNullable(DartType type) {
       expect(typeSystem.isNonNullable(type), isTrue);
     }
  
positive.code: }
  
  @reflectiveTest
  class IsNullableTest extends _NullableBase {
    void isNotNullable(DartType type) {
      expect(typeSystem.isNullable(type), isFalse);
    }
  
negative.code: }
  
  @reflectiveTest
  class PromoteToNonNullTest extends AbstractTypeSystemNullSafetyTest {
    test_dynamic() {
      _check(dynamicType, dynamicType);
    }
  