Make sure pub build/serve get at the right time:

sdk/lib/_internal/pub/test/serve/utils.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS d.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:async';
 import 'dart:convert';
 import 'dart:io';
 
@@ skipping 96 matching lines @@
   // Dart2js can take a long time to compile dart code, so we increase the
   // timeout to cope with that.
   currentSchedule.timeout = new Duration(seconds: 15);
 
   return startPub(args: pubArgs);
 }
 
 /// Schedules starting the "pub serve" process and records its port number for
 /// future requests.
 ///
-/// If [shouldGetFirst] is `true`, validates that pub get is run first.
+/// If [shouldGetFirst] is `true`, validates that pub get is run first. In that
+/// case, you can also pass [numDownloads] to specify how many packages should
+/// be downloaded during the get.
 ///
 /// Returns the `pub serve` process.
 ScheduledProcess pubServe({bool shouldGetFirst: false,
-    Iterable<String> args}) {
+    Iterable<String> args, int numDownloads: 0}) {
   _pubServer = startPubServe(args);
 
   currentSchedule.onComplete.schedule(() {
     if (_webSocket != null) {
       _webSocket.close();
       _webSocket = null;
       _webSocketBroadcastStream = null;
     }
   });
 
   if (shouldGetFirst) {
     expect(_pubServer.nextLine(),
         completion(anyOf(
              startsWith("Your pubspec has changed"),
-             startsWith("You don't have a lockfile"))));
+             startsWith("You don't have a lockfile"),
+             startsWith("You are missing some dependencies"))));
     expect(_pubServer.nextLine(),
         completion(startsWith("Resolving dependencies...")));
+
+    for (var i = 0; i < numDownloads; i++) {
+      expect(_pubServer.nextLine(),
+          completion(startsWith("Downloading")));
+    }
+
     expect(_pubServer.nextLine(),
         completion(equals("Got dependencies!")));
   }
 
   expect(_pubServer.nextLine().then(_parsePort), completes);
   return _pubServer;
 }
 
 /// Parses the port number from the "Serving blah on 127.0.0.1:1234" line
 /// printed by pub serve.
@@ skipping 82 matching lines @@
 /// socket. It omitted, request is JSON encoded to a string first.
 void webSocketShouldReply(request, expectation, {bool encodeRequest: true}) {
   schedule(() => _ensureWebSocket().then((_) {
     if (encodeRequest) request = JSON.encode(request);
     _webSocket.add(request);
     return _webSocketBroadcastStream.first.then((value) {
       expect(JSON.decode(value), expectation);
     });
   }), "send $request to web socket and expect reply that $expectation");
 }