Run test tearDowns and clean up temporary directories when a signal is caught.

test/runner/test_on_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/util/io.dart';
 import 'package:test/test.dart';
 
 import '../io.dart';
 
 String _sandbox;
 
 final _otherOS = Platform.isWindows ? "mac-os" : "windows";
 
 void main() {
   setUp(() {
-    _sandbox = Directory.systemTemp.createTempSync('test_').path;
+    _sandbox = createTempDir();
   });
 
   tearDown(() {
     new Directory(_sandbox).deleteSync(recursive: true);
   });
 
   group("for suite", () {
     test("runs a test suite on a matching platform", () {
       _writeTestFile("vm_test.dart", suiteTestOn: "vm");
 
@@ skipping 176 matching lines @@
     buffer.writeln("  });");
   }
 
   buffer.writeln("}");
 
   new File(p.join(_sandbox, filename)).writeAsStringSync(buffer.toString());
 }
 
 ProcessResult _runUnittest(List<String> args) =>
     runUnittest(args, workingDirectory: _sandbox);