Add a filesystem descriptor library to scheduled_test.

pkg/scheduled_test/lib/descriptor.dart

Index: pkg/scheduled_test/lib/descriptor.dart
diff --git a/pkg/scheduled_test/lib/descriptor.dart b/pkg/scheduled_test/lib/descriptor.dart
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+// 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 [Entry.create] to schedule a task that will create that structure on
+/// the physical filesystem, or [Entry.validate] to schedule an assertion that
+/// that structure exists. For example:
+///
+///     import 'package:scheduled_test/descriptor.dart' as d;
+///     import 'package:scheduled_test/scheduled_test.dart';
+///
+///     void main() {
+///       test('Directory.rename', () {
+///         d.dir('parent', [
+///           d.file('sibling', 'sibling-contents'),
+///           d.dir('old-name', [
+///             d.file('child', 'child-contents')
+///           ])
+///         ]).create();
+///
+///         schedule(() =>
+///             new Directory('parent/old-name').rename('parent/new-name'));
+///
+///         d.dir('parent', [
+///           d.file('sibling', 'sibling-contents'),
+///           d.dir('new-name', [
+///             d.file('child', 'child-contents')
+///           ])
+///         ]).validate();
+///       })
+///     }
+///
+/// Usually you don't want your tests cluttering up your working directory with
+/// fake filesystem entities. You can set [defaultRoot] to configure where
+/// 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) {
+///             tempDir = dir;
+///             d.defaultRoot = tempDir.path;
+///           });
+///         });
+///
+///         currentSchedule.onComplete.schedule(() {
+///           d.defaultRoot = null;
+///           return tempDir.delete(recursive: true);
+///         });
+///       });
+///
+///       // ...
+///     }
+library descriptor;
+
+import 'dart:async';
+
+import 'package:pathos/path.dart' as path;
+
+import 'scheduled_test.dart';
+import 'src/descriptor/directory.dart';
+import 'src/descriptor/entry.dart';
+import 'src/descriptor/file.dart';
+
+export 'src/descriptor/directory.dart';
+export 'src/descriptor/entry.dart';
+export 'src/descriptor/file.dart';
+
+/// The root path for descriptors. Top-level descriptors will be created and
+/// validated at this path. Defaults to the current working directory.
+///
+/// If this is set to `null`, it will reset itself to the current working
+/// directory.
+String get defaultRoot => _defaultRoot == null ? path.current : _defaultRoot;
+set defaultRoot(String value) {
+  _defaultRoot = value;
+}
+String _defaultRoot;
+
+/// Creates a new text [File] descriptor with [name] and [contents].
+File file(Pattern name, [String contents='']) => new File(name, contents);
+
+/// Creates a new binary [File] descriptor with [name] and [contents].
+File binaryFile(Pattern name, List<int> contents) =>
+    new File.binary(name, contents);
+
+/// Creates a new [Directory] descriptor with [name] and [contents].
+Directory dir(Pattern name, [Iterable<Entry> contents]) =>
+    new Directory(name, contents == null ? <Entry>[] : contents);