add --preview flag to publish command

utils/tests/pub/pub_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 pub_tests;
 
 import 'dart:io';
 
 import 'test_pub.dart';
 import '../../../pkg/unittest/lib/unittest.dart';
@@ skipping 87 matching lines @@
             Usage: pub install
             ''');
     });
 
     integration('shows help for a command', () {
       schedulePub(args: ['help', 'publish'],
           output: '''
             Publish the current package to pub.dartlang.org.
 
             Usage: pub publish [options]
-            --server    The package server to which to upload this package
-                        (defaults to "https://pub.dartlang.org")
+            -n, --dry-run    Preview publishing the package
+                             Validate but do not publish the package
+
+                --server     The package server to which to upload this package
+                             (defaults to "https://pub.dartlang.org")
             ''');
     });
 
     integration('an unknown help command displays an error message', () {
       schedulePub(args: ['help', 'quylthulg'],
           error: '''
             Could not find a command named "quylthulg".
             Run "pub help" to see available commands.
             ''',
             exitCode: 64);
@@ skipping 18 matching lines @@
       // The "version" file generated on developer builds is a little funky and
       // we need to make sure we don't choke on it.
       dir(sdkPath, [
         file('version', '0.1.2.0_r16279_bobross'),
       ]).scheduleCreate();
 
       schedulePub(args: ['version'], output: "Pub 0.1.2+0.r16279.bobross\n");
     });
   });
 }