anchor.diff:  
   main() {
     defineReflectiveSuite(() {
  -    defineReflectiveTests(ProvisionalApiTest);
  -    defineReflectiveTests(ProvisionalApiTestPermissive);
  -    defineReflectiveTests(ProvisionalApiTestWithReset);
  +    defineReflectiveTests(_ProvisionalApiTest);
  +    defineReflectiveTests(_ProvisionalApiTestPermissive);
  +    defineReflectiveTests(_ProvisionalApiTestWithReset);
     });
   }
   
   /// Tests of the provisional API.
   @reflectiveTest
  -class ProvisionalApiTest extends ProvisionalApiTestBase
  -    with ProvisionalApiTestCases {
  +class _ProvisionalApiTest extends _ProvisionalApiTestBase
  +    with _ProvisionalApiTestCases {
     @override
  -  bool get usePermissiveMode => false;
  +  bool get _usePermissiveMode => false;
   }
   
   /// Base class for provisional API tests.
  -abstract class ProvisionalApiTestBase extends AbstractContextTest {
  -  bool get usePermissiveMode;
  +abstract class _ProvisionalApiTestBase extends AbstractContextTest {
  +  bool get _usePermissiveMode;
   
     /// Hook invoked after calling `prepareInput` on each input.
     void _afterPrepare() {}
  
positive.code: }
  
  @reflectiveTest
  class ProvisionalApiTestPermissive extends ProvisionalApiTestBase
      with ProvisionalApiTestCases {
    @override
    bool get usePermissiveMode => true;
  }
  
  /// Tests of the provisional API, where the driver is reset between calls to
  /// `prepareInput` and `processInput`, ensuring that the migration algorithm
  /// sees different AST and element objects during different phases.
  @reflectiveTest
  class ProvisionalApiTestWithReset extends ProvisionalApiTestBase
      with ProvisionalApiTestCases {
    @override
    bool get usePermissiveMode => false;
  
    @override
    void _afterPrepare() {
  
negative.code: }
  
  /// Mixin containing test cases for the provisional API.
  mixin _ProvisionalApiTestCases on _ProvisionalApiTestBase {
    test_conditional_assert_statement_does_not_imply_non_null_intent() async {
      var content = '''
  void f(bool b, int i) {
  