Switch from unittest to test.

test/markdown_test.dart

 // Copyright (c) 2011, 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.
 
 /// Unit tests for markdown.
 library markdown.test.markdown_test;
 
-import 'package:unittest/unittest.dart';
+import 'package:test/test.dart';
 
 import 'package:markdown/markdown.dart';
 
 import 'util.dart';
 
 /// Most of these tests are based on observing how showdown behaves:
 /// http://softwaremaniacs.org/playground/showdown-highlight/
 void main() {
   group('Paragraphs', () {
     validate(
@@ skipping 1379 matching lines @@
         'ignores block-level markdown syntax',
         '''
         1. This will not be an <ol>.
         ''',
         '''
         1. This will not be an &lt;ol>.
         ''',
         inlineOnly: true);
   });
 }