Use the VM to detect when a precompiled executable is out-of-date.

sdk/lib/_internal/pub/test/test_pub.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.
 
 /// Test infrastructure for testing pub.
 ///
 /// Unlike typical unit tests, most pub tests are integration tests that stage
 /// some stuff on the file system, run pub, and then validate the results. This
 /// library provides an API to build tests like that.
 library test_pub;
@@ skipping 807 matching lines @@
     "author": "Natalie Weizenbaum <nweiz@google.com>",
     "homepage": "http://pub.dartlang.org",
     "description": "A package, I guess."
   };
 
   if (dependencies != null) package["dependencies"] = dependencies;
 
   return package;
 }
 
+/// Resolves [target] relative to the path to pub's `test/asset` directory.
+String testAssetPath(String target) =>
+    p.join(p.dirname(libraryPath('test_pub')), 'asset', target);
+
 /// Returns a Map in the format used by the pub.dartlang.org API to represent a
 /// package version.
 ///
 /// [pubspec] is the parsed pubspec of the package version. If [full] is true,
 /// this returns the complete map, including metadata that's only included when
 /// requesting the package version directly.
 Map packageVersionApiMap(Map pubspec, {bool full: false}) {
   var name = pubspec['name'];
   var version = pubspec['version'];
   var map = {
@@ skipping 141 matching lines @@
         _lastMatcher.matches(item.last, matchState);
   }
 
   Description describe(Description description) {
     return description.addAll("(", ", ", ")", [_firstMatcher, _lastMatcher]);
   }
 }
 
 /// A [StreamMatcher] that matches multiple lines of output.
 StreamMatcher emitsLines(String output) => inOrder(output.split("\n"));