Use the package_resolver package.

test/runner/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")
 
 import 'dart:io';
 
 import 'package:path/path.dart' as p;
 import 'package:test/src/backend/state.dart';
@@ skipping 15 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(packageRoot: p.join(packageDir, 'packages')),
+        new Configuration(),
         root: _sandbox);
   });
 
   tearDown(() {
     new Directory(_sandbox).deleteSync(recursive: true);
     return _loader.close();
   });
 
   group(".loadFile()", () {
     var suite;
@@ skipping 105 matching lines @@
     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);
   });
 
   // TODO: Test load suites. Don't forget to test that prints in loaded files
   // are piped through the suite. Also for browser tests!
 }