anchor.diff:  
     test_deadBlock_if_debugConst_propertyAccessor() async {
       newFile('/test/lib/lib2.dart', content: r'''
  -library lib2;
   class A {
     static const bool DEBUG = false;
   }''');
       await assertNoErrorsInCode(r'''
  -library L;
   import 'lib2.dart' as LIB;
   f() {
     if(LIB.A.DEBUG) {}
  
positive.code: 
    test_assignCompound_nonNullable() async {
      await assertErrorsInCode(r'''
  @pragma('analyzer:non-nullable')
  library foo;
  
  m(int x) {
    x ??= 1;
  }
  ''', [
        error(HintCode.DEAD_CODE, 66, 1),
      ]);
    }
  
    test_assignCompound_nullable() async {
      await assertNoErrorsInCode(r'''
  @pragma('analyzer:non-nullable')
  library foo;
  
  m() {
    int? x;
    x ??= 1;
  
negative.code: 
    test_binary_nonNullable() async {
      await assertErrorsInCode(r'''
  m(int x) {
    x ?? 1;
  }
  ''', [
        error(HintCode.DEAD_CODE, 18, 1),
      ]);
    }
  
    test_binary_nullable() async {
      await assertNoErrorsInCode(r'''
  m() {
    int? x;
    x ?? 1;
  