Use an auto-generated pub snapshot for tests.

lib/src/io.dart

 // Copyright (c) 2013, 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.
 
 /// Helper functionality to make working with IO easier.
 library pub.io;
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:convert';
@@ skipping 459 matching lines @@
   // symlink to.
   target = path.join(target, 'lib');
   if (!dirExists(target)) return;
 
   log.fine("Creating ${isSelfLink ? "self" : ""}link for package '$name'.");
   createSymlink(target, symlink, relative: relative);
 }
 
 /// Whether pub is running from within the Dart SDK, as opposed to from the Dart
 /// source repository.
-final bool runningFromSdk = Platform.script.path.endsWith('.snapshot');
+final bool runningFromSdk = Platform.script.path.endsWith('.dart.snapshot');
 
 /// Resolves [target] relative to the path to pub's `asset` directory.
 String assetPath(String target) {
   if (runningFromSdk) {
     return path.join(
         sdk.rootDirectory, 'lib', '_internal', 'pub', 'asset', target);
   } else {
     return path.join(pubRoot, 'asset', target);
   }
 }
@@ skipping 519 matching lines @@
 
   // TODO(rnystrom): Remove this and change to returning one string.
   static List<String> _toLines(String output) {
     var lines = splitLines(output);
     if (!lines.isEmpty && lines.last == "") lines.removeLast();
     return lines;
   }
 
   bool get success => exitCode == exit_codes.SUCCESS;
 }