Tweak the concurrency settings a bit and release.

lib/src/runner/engine.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.
 
 library test.runner.engine;
 
 import 'dart:async';
 import 'dart:collection';
 
 import 'package:async/async.dart' hide Result;
@@ skipping 126 matching lines @@
   final _activeLoadTests = new List<LiveTest>();
 
   /// Creates an [Engine] that will run all tests provided via [suiteSink].
   ///
   /// [concurrency] controls how many suites are run at once, and defaults to 1.
   /// [maxSuites] controls how many suites are *loaded* at once, and defaults to
   /// four times [concurrency].
   Engine({int concurrency, int maxSuites})
       : _runPool = new Pool(concurrency == null ? 1 : concurrency),
         _loadPool = new Pool(maxSuites == null
-            ? (concurrency == null ? 4 : concurrency * 4)
+            ? (concurrency == null ? 2 : concurrency * 2)
             : maxSuites) {
     _group.future.then((_) {
       if (_closedBeforeDone == null) _closedBeforeDone = false;
     }).catchError((_) {
       // Don't top-level errors. They'll be thrown via [success] anyway.
     });
   }
 
   /// Creates an [Engine] that will run all tests in [suites].
   ///
@@ skipping 161 matching lines @@
 
     // Close the running tests first so that we're sure to wait for them to
     // finish before we close their suites and cause them to become unloaded.
     var allLiveTests = liveTests.toSet()..addAll(_activeLoadTests);
     await Future.wait(allLiveTests.map((liveTest) => liveTest.close()));
 
     var allSuites = allLiveTests.map((liveTest) => liveTest.suite).toSet();
     await Future.wait(allSuites.map((suite) => suite.close()));
   }
 }