Only load a certain number of test suites at once.

lib/src/backend/suite.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.backend.suite;
 
+import 'dart:async';
 import 'dart:collection';
 
+import '../util/async_thunk.dart';
+import '../utils.dart';
 import 'metadata.dart';
 import 'operating_system.dart';
 import 'test.dart';
 import 'test_platform.dart';
 
 /// A test suite.
 ///
 /// A test suite is a set of tests that are intended to be run together and that
 /// share default configuration.
 class Suite {
   /// A description of the platform on which the suite is running, or `null` if
   /// that platform is unknown.
   final String platform;
 
   /// The path to the Dart test suite, or `null` if that path is unknown.
   final String path;
 
   /// The metadata associated with this test suite.
   final Metadata metadata;
 
+  /// The thunk for running [close] exactly once.
+  final _closeThunk = new AsyncThunk();
+
+  /// The function to call when the suite is closed.
+  final AsyncFunction _onClose;
+
   /// The tests in the test suite.
   final List<Test> tests;
 
-  Suite(Iterable<Test> tests, {this.path, this.platform, Metadata metadata})
+  Suite(Iterable<Test> tests, {this.path, this.platform, Metadata metadata,
+          AsyncFunction onClose})
       : metadata = metadata == null ? new Metadata() : metadata,
+        _onClose = onClose,
         tests = new UnmodifiableListView<Test>(tests.toList());
 
   /// Returns a view of this suite for the given [platform] and [os].
   ///
   /// This filters out tests that are invalid for [platform] and [os] and
   /// resolves platform-specific metadata. If the suite itself is invalid for
   /// [platform] and [os], returns `null`.
   Suite forPlatform(TestPlatform platform, {OperatingSystem os}) {
     if (!metadata.testOn.evaluate(platform, os: os)) return null;
     return change(tests: tests.where((test) {
       return test.metadata.testOn.evaluate(platform, os: os);
     }).map((test) {
       return test.change(metadata: test.metadata.forPlatform(platform, os: os));
     }), metadata: metadata.forPlatform(platform, os: os));
   }
 
   /// Returns a new suite with the given fields updated.
   Suite change({String path, String platform, Metadata metadata,
       Iterable<Test> tests}) {
     if (path == null) path = this.path;
     if (platform == null) platform = this.platform;
     if (metadata == null) metadata = this.metadata;
     if (tests == null) tests = this.tests;
-    return new Suite(tests, path: path, platform: platform, metadata: metadata);
+    return new Suite(tests, path: path, platform: platform, metadata: metadata,
+        onClose: this.close);
+  }
+
+  /// Closes the suite and releases any resources associated with it.
+  Future close() {
+    return _closeThunk.run(() async {
+      if (_onClose != null) await _onClose();
+    });
   }
 }