add a repro for #136 (#160)

Author: devoncarew

test/repro_136_test.dart

@@ -0,0 +1,38 @@
+// Copyright (c) 2023, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:csslib/parser.dart';
+import 'package:csslib/visitor.dart';
+import 'package:test/test.dart';
+
+const options = PreprocessorOptions(
+  useColors: false,
+  warningsAsErrors: true,
+  inputFile: 'memory',
+);
+
+void main() {
+  test('repro_136', () {
+    // Repro test for https://github.com/dart-lang/csslib/issues/136.
+    final errors = <Message>[];
+
+    final css = '''
+.hero.is-white a:not(.button):not(.dropdown-item):not(.tag):not(.pagination-link.is-current),
+.hero.is-white strong {
+  color: inherit;
+}
+''';
+    final stylesheet = parse(css, errors: errors, options: options);
+    expect(stylesheet.topLevels, hasLength(1));
+    var ruleset = stylesheet.topLevels.first as RuleSet;
+
+    // This should be length 2.
+    expect(ruleset.selectorGroup!.selectors, hasLength(1));
+
+    // This test is expected to start to fail once we better support pseudo
+    // selectors.
+    // This should be empty.
+    expect(errors, hasLength(3));
+  });
+}