anchor.diff:  
         expect(printStyleSheet(sheet, pretty: false),
             '.red,.blue { color: red; } .blue { width: 0; }');
  +    });
  +
  +    test('extend_bug_media_query', () {
  +      String input;
  +      String generated;
  +
  +      // extend works when a a single definition is used
  +      input =
  +          '.good { color: red; } @media screen { .better { @extend .good; } }';
  +      generated = '.good,.better { color: red; } @media screen { .better { } }';
  +      // it should be: '.good { color: red; } @media screen { .better { color: red; } }
  +      checkPolyfill(input, generated);
  +    });
  +
  +    test('extend_bug_multi_selector', () {
  +      String input;
  +      String generated;
  +
  +      // extend works when a a single definition is used
  +      input = '.good { color: red; } .better { @extend .good; }';
  +      generated = '.good,.better { color: red; } .better { }';
  +      checkPolyfill(input, generated);
  +
  +      // but not if use
  +      input = '.good { color: red; } .better,.best { @extend .good; }';
  +      generated = '.good,.better { color: red; } .better,.best { }';
  +      // it should be: generated = '.good,.better,.best { color: red; } .better,.best { }';
  +      checkPolyfill(input, generated);
       });
   
       test('scss_media_query_var_and_extend', () {
  
positive.code:     });
  
      test('simple_css3_var_no_polyfill', () {
        String css = '''
  :host {
    --test-color1: red;
  }
  body {
    color: var(--test-color1);
  }''';
        StyleSheet sheet = compile(css);
  
        expect(printStyleSheet(sheet, pretty: false),
            ':host { --test-color1: red; } body { color: var(--test-color1); }');
      });
  
      test('simple_css3', () {
        // css3 vars not working
        String css = '''
  :host {
    --test-color1: red;
  }
  body {
    color: var(--test-color1);
  }''';
        StyleSheet sheet = compile(css,
            options: new PreprocessorOptions(polyfill: true), polyfill: true);
  
        expect(printStyleSheet(sheet, pretty: false),
            ':host { --test-color1: red; } body { color: ; }');
      });
  
      test('nested_rule', () {
  
negative.code:           compileCss('@color1: red; body { color: @color1; }', pretty: false),
            'body { color: red; }');
      });
      test('less_@', () {
        String css = 'body{opacity:1}';
        expect(compileCss(css), compileCss(css, polyfill: false));
        css = '@color1: red; body { color: @color1; }';
        expect(compileCss(css), isNot(compileCss(css, polyfill: false)));
      });
  
      test('less_var', () {
        final input = '''
  @color-background: red;
  @color-foreground: blue;
  .test {
    background-color: var(color-background);
    color: var(color-foreground);
  }
  ''';
        final generated = '''
  var-color-background: #f00;
  var-color-foreground: #00f;
  
  .test {
    background-color: var(color-background);
    color: var(color-foreground);
  }''';
        checkCompile(input, generated, pretty: true);
      });
    });
    //YachtTransformer transformer;
    group('csslib_exp', () {
  