Fix several problems with offline mode.

test/hosted/offline_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 'package:pub/src/exit_codes.dart' as exit_codes;
+
 import '../descriptor.dart' as d;
 import '../test_pub.dart';
 
 main() {
   forBothPubGetAndUpgrade((command) {
     integration('upgrades a package using the cache', () {
       // Run the server so that we know what URL to use in the system cache.
-      serveNoPackages();
+      serveErrors();
 
       d.cacheDir({
         "foo": ["1.2.2", "1.2.3"],
         "bar": ["1.2.3"]
       }, includePubspecs: true).create();
 
       d.appDir({
         "foo": "any",
         "bar": "any"
       }).create();
 
       var warning = null;
       if (command == RunCommand.upgrade) {
         warning = "Warning: Upgrading when offline may not update you "
                   "to the latest versions of your dependencies.";
       }
 
       pubCommand(command, args: ['--offline'], warning: warning);
 
       d.packagesDir({
         "foo": "1.2.3",
         "bar": "1.2.3"
       }).validate();
     });
 
     integration('fails gracefully if a dependency is not cached', () {
       // Run the server so that we know what URL to use in the system cache.
-      serveNoPackages();
+      serveErrors();
 
       d.appDir({"foo": "any"}).create();
 
       pubCommand(command, args: ['--offline'],
-          error: "Could not find package foo in cache.");
+          exitCode: exit_codes.UNAVAILABLE,
+          error: "Could not find package foo in cache.\n"
+                 "Depended on by:\n"
+                 "- myapp");
     });
 
-    integration('fails gracefully no cached versions match', () {
+    integration('fails gracefully if no cached versions match', () {
       // Run the server so that we know what URL to use in the system cache.
-      serveNoPackages();
+      serveErrors();
 
       d.cacheDir({
         "foo": ["1.2.2", "1.2.3"]
       }, includePubspecs: true).create();
 
       d.appDir({"foo": ">2.0.0"}).create();
 
       pubCommand(command, args: ['--offline'], error:
           "Package foo has no versions that match >2.0.0 derived from:\n"
           "- myapp depends on version >2.0.0");
     });
+
+    integration('fails gracefully if a dependency is not cached and a lockfile '
+        'exists', () {
+      // Run the server so that we know what URL to use in the system cache.
+      serveErrors();
+
+      d.appDir({"foo": "any"}).create();
+
+      createLockFile('myapp', hosted: {'foo': '1.2.4'});
+
+      pubCommand(command, args: ['--offline'],
+          exitCode: exit_codes.UNAVAILABLE,
+          error: "Could not find package foo in cache.\n"
+                 "Depended on by:\n"
+                 "- myapp");
+    });
+
+    integration('downgrades to the version in the cache if necessary', () {
+      // Run the server so that we know what URL to use in the system cache.
+      serveErrors();
+
+      d.cacheDir({
+        "foo": ["1.2.2", "1.2.3"]
+      }, includePubspecs: true).create();
+
+      d.appDir({"foo": "any"}).create();
+
+      createLockFile('myapp', hosted: {'foo': '1.2.4'});
+
+      pubCommand(command, args: ['--offline']);
+
+      d.packagesDir({"foo": "1.2.3"}).validate();
+    });
   });
 }