Install before starting the server if the lockfile is out of date.

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:io';
 
 import 'package:http/http.dart' as http;
 import 'package:scheduled_test/scheduled_process.dart';
 import 'package:scheduled_test/scheduled_test.dart';
 
 import '../descriptor.dart' as d;
 import '../test_pub.dart';
 
 /// The pub process running "pub serve".
 ScheduledProcess _pubServer;
 
 /// The ephemeral port assigned to the running server.
 int _port;
 
 /// Schedules starting the "pub serve" process.
-void startPubServe() {
+///
+/// If [shouldInstallFirst] is `true`, validates that pub install is run first.
+void startPubServe({bool shouldInstallFirst: false}) {
   // Use port 0 to get an ephemeral port.
   _pubServer = startPub(args: ["serve", "--port=0"]);
 
-  expect(_pubServer.nextLine().then((line) {
-    var match = new RegExp(r"localhost:(\d+)").firstMatch(line);
-    assert(match != null);
-    _port = int.parse(match[1]);
-  }), completes);
+  if (shouldInstallFirst) {
+    expect(_pubServer.nextLine(),
+        completion(startsWith("Dependencies have changed")));
+    expect(_pubServer.nextLine(),
+        completion(startsWith("Resolving dependencies...")));
+    expect(_pubServer.nextLine(),
+        completion(equals("Dependencies installed!")));
+  }
+
+  expect(_pubServer.nextLine().then(_parsePort), completes);
+}
+
+/// Parses the port number from the "Serving blah on localhost:1234" line
+/// printed by pub serve.
+void _parsePort(String line) {
+  var match = new RegExp(r"localhost:(\d+)").firstMatch(line);
+  assert(match != null);
+  _port = int.parse(match[1]);
 }
 
 void endPubServe() {
   _pubServer.kill();
 }
 
 /// Schedules an HTTP request to the running pub server with [urlPath] and
 /// verifies that it responds with [expected].
 void requestShouldSucceed(String urlPath, String expected) {
   schedule(() {
     return http.get("http://localhost:$_port/$urlPath").then((response) {
       expect(response.body, equals(expected));
     });
   }, "request $urlPath");
 }
 
 /// Schedules an HTTP request to the running pub server with [urlPath] and
 /// verifies that it responds with a 404.
 void requestShould404(String urlPath) {
   schedule(() {
     return http.get("http://localhost:$_port/$urlPath").then((response) {
       expect(response.statusCode, equals(404));
     });
   }, "request $urlPath");
 }