Use the package_resolver package.

test/runner/loader_test.dart

Index: test/runner/loader_test.dart
diff --git a/test/runner/loader_test.dart b/test/runner/loader_test.dart
index f93bae9c24b11709d831789283c6fb3fb046a24d..182d2e2f74c93ec9a0dab6b8e94651efc9a30908 100644
--- a/test/runner/loader_test.dart
+++ b/test/runner/loader_test.dart
@@ -33,10 +33,10 @@ void main() {
 """;
 
 void main() {
-  setUp(() {
+  setUp(() async {
     _sandbox = createTempDir();
     _loader = new Loader(
-        new Configuration(packageRoot: p.join(packageDir, 'packages')),
+        new Configuration(),
         root: _sandbox);
   });