Upgrade to test 0.12.0.

test/args_test.dart

 // Copyright (c) 2012, 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 args_test;
 
-import 'package:unittest/unittest.dart';
+import 'package:test/test.dart';
 import 'package:args/args.dart';
 import 'utils.dart';
 
 void main() {
   group('ArgParser.addFlag()', () {
     test('throws ArgumentError if the flag already exists', () {
       var parser = new ArgParser();
       parser.addFlag('foo');
       throwsIllegalArg(() => parser.addFlag('foo'));
     });
@@ skipping 293 matching lines @@
 const _VALID_OPTIONS = const [
   'a', // One character.
   'contains-dash',
   'contains_underscore',
   'ends-with-dash-',
   'contains--doubledash--',
   '1starts-with-number',
   'contains-a-1number',
   'ends-with-a-number8'
 ];