Upgrade to test 0.12.0.

test/command_test.dart

 // Copyright (c) 2014, 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 command_test;
 
 import 'package:args/command_runner.dart';
-import 'package:unittest/unittest.dart';
+import 'package:test/test.dart';
 import 'utils.dart';
 
 void main() {
   var foo;
   setUp(() {
     foo = new FooCommand();
 
     // Make sure [Command.runner] is set up.
     new CommandRunner("test", "A test command runner.").addCommand(foo);
   });
@@ skipping 78 matching lines @@
 -h, --help    Print this usage information.
 
 Run "test help" to see global options."""));
   });
 
   test("considers a command hidden if all its subcommands are hidden", () {
     foo.addSubcommand(new HiddenCommand());
     expect(foo.hidden, isTrue);
   });
 }