Use helper methods for running pub.

sdk/lib/_internal/pub/test/install/hosted/resolve_constraints_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 'dart:io';
 
 import '../../descriptor.dart' as d;
 import '../../test_pub.dart';
 
 main() {
   initConfig();
   integration('resolves version constraints from a pub server', () {
     servePackages([
       packageMap("foo", "1.2.3", [dependencyMap("baz", ">=2.0.0")]),
       packageMap("bar", "2.3.4", [dependencyMap("baz", "<3.0.0")]),
       packageMap("baz", "2.0.3"),
       packageMap("baz", "2.0.4"),
       packageMap("baz", "3.0.1")
     ]);
 
     d.appDir([dependencyMap("foo"), dependencyMap("bar")]).create();
 
-    schedulePub(args: ['install'],
-        output: new RegExp("Dependencies installed!\$"));
+    pubInstall();
 
     d.cacheDir({
       "foo": "1.2.3",
       "bar": "2.3.4",
       "baz": "2.0.4"
     }).validate();
 
     d.packagesDir({
       "foo": "1.2.3",
       "bar": "2.3.4",
       "baz": "2.0.4"
     }).validate();
   });
 }