Use Directory.systemTemp getter in pkg subdirectory of repository.

pkg/scheduled_test/lib/descriptor.dart

 // Copyright (c) 2013, 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.
 
 /// A library for declaratively describing a filesystem structure, usually for
 /// the purpose of creating or validating it as part of a scheduled test.
 ///
 /// You can use [dir] and [file] to define a filesystem structure. Then, you can
 /// call [Descriptor.create] to schedule a task that will create that structure
 /// on the physical filesystem, or [Descriptor.validate] to schedule an
@@ skipping 28 matching lines @@
 /// filesystem descriptors are rooted on the physical filesystem. For example,
 /// to create a temporary directory for each test:
 ///
 ///     import 'package:scheduled_test/descriptor.dart' as d;
 ///     import 'package:scheduled_test/scheduled_test.dart';
 ///
 ///     void main() {
 ///       setUp(() {
 ///         var tempDir;
 ///         schedule(() {
-///           return new Directory('').createTemp().then((dir) {
+///           return Directory.systemTemp
+///                           .createTemp('my_temp_dir_')
+///                           .then((dir) {
 ///             tempDir = dir;
 ///             d.defaultRoot = tempDir.path;
 ///           });
 ///         });
 ///
 ///         currentSchedule.onComplete.schedule(() {
 ///           d.defaultRoot = null;
 ///           return tempDir.delete(recursive: true);
 ///         });
 ///       });
@@ skipping 73 matching lines @@
 
 /// A convenience method for creating a [PatternDescriptor] descriptor that
 /// constructs a [FileDescriptor] descriptor.
 PatternDescriptor filePattern(Pattern name, [String contents='']) =>
   pattern(name, (realName) => file(realName, contents));
 
 /// A convenience method for creating a [PatternDescriptor] descriptor that
 /// constructs a [DirectoryDescriptor] descriptor.
 PatternDescriptor dirPattern(Pattern name, [Iterable<Descriptor> contents]) =>
   pattern(name, (realName) => dir(realName, contents));