Switch from unittest to test.

test/util.dart

 // Copyright (c) 2015, 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.
 
 library markdown.test.utils;
 
-import 'package:unittest/unittest.dart';
+import 'package:test/test.dart';
 
 import 'package:markdown/markdown.dart';
 
 /// Removes eight spaces of leading indentation from a multiline string.
 ///
 /// Note that this is very sensitive to how the literals are styled. They should
 /// be:
 ///     '''
 ///     Text starts on own line. Lines up with subsequent lines.
 ///     Lines are indented exactly 8 characters from the left margin.'''
@@ skipping 68 matching lines @@
 
     // If one string runs out of non-ignored strings, the other must too.
     if (i == a.length) return j == b.length;
     if (j == b.length) return i == a.length;
 
     if (a[i] != b[j]) return false;
     i++;
     j++;
   }
 }