Use the package_resolver package.

test/runner/browser/loader_test.dart

 // Copyright (c) 2015, 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.
 
 @TestOn("vm")
 @Tags(const ["chrome"])
 
 import 'dart:io';
 
 import 'package:path/path.dart' as p;
@@ skipping 16 matching lines @@
 import 'package:test/test.dart';
 
 void main() {
   test("success", () {});
   test("failure", () => throw new TestFailure('oh no'));
   test("error", () => throw 'oh no');
 }
 """;
 
 void main() {
-  setUp(() {
+  setUp(() async {
     _sandbox = createTempDir();
-    _loader = new Loader(new Configuration(
-            platforms: [TestPlatform.chrome],
-            packageRoot: p.join(packageDir, 'packages')),
+    _loader = new Loader(new Configuration(platforms: [TestPlatform.chrome]),
         root: _sandbox);
     /// TODO(nweiz): Use scheduled_test for this once it's compatible with this
     /// version of test.
     new File(p.join(_sandbox, 'a_test.dart')).writeAsStringSync(_tests);
   });
 
   tearDown(() {
     new Directory(_sandbox).deleteSync(recursive: true);
     return _loader.close();
   });
@@ skipping 68 matching lines @@
     var loadSuite = suites.first;
     var suite = await loadSuite.getSuite();
     expect(suite.group.entries, hasLength(3));
     expect(suite.group.entries[0].name, equals("success"));
     expect(suite.group.entries[1].name, equals("failure"));
     expect(suite.group.entries[2].name, equals("error"));
   });
 
   test("loads a suite both in the browser and the VM", () async {
     var loader = new Loader(
-        new Configuration(
-            platforms: [TestPlatform.vm, TestPlatform.chrome],
-            packageRoot: p.join(packageDir, 'packages')),
+        new Configuration(platforms: [TestPlatform.vm, TestPlatform.chrome]),
         root: _sandbox);
     var path = p.join(_sandbox, 'a_test.dart');
 
     try {
       var suites = await loader.loadFile(path)
           .asyncMap((loadSuite) => loadSuite.getSuite()).toList();
       expect(suites[0].platform, equals(TestPlatform.vm));
       expect(suites[0].path, equals(path));
       expect(suites[1].platform, equals(TestPlatform.chrome));
       expect(suites[1].path, equals(path));
@@ skipping 20 matching lines @@
     expect(suites, hasLength(1));
     var loadSuite = suites.first;
 
     var liveTest = await loadSuite.group.entries.single.load(loadSuite);
     expect(liveTest.onMessage.first.then((message) => message.text),
         completion(equals("print within test")));
     await liveTest.run();
     expectTestPassed(liveTest);
   });
 }