Add a CommandRunner class for dispatching commands to args.

pkg/args/test/utils.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.
 
 library utils;
 
+import 'dart:async';
+
+import 'package:args/args.dart';
+import 'package:args/command_runner.dart';
 import 'package:unittest/unittest.dart';
-import 'package:args/args.dart';
+
+class FooCommand extends Command {
+  var hasRun = false;
+
+  final name = "foo";
+  final description = "Set a value.";
+  final takesArguments = false;
+
+  void run() {
+    hasRun = true;
+  }
+}
+
+class HiddenCommand extends Command {
+  var hasRun = false;
+
+  final name = "hidden";
+  final description = "Set a value.";
+  final hidden = true;
+  final takesArguments = false;
+
+  void run() {
+    hasRun = true;
+  }
+}
+
+class AliasedCommand extends Command {
+  var hasRun = false;
+
+  final name = "aliased";
+  final description = "Set a value.";
+  final takesArguments = false;
+  final aliases = const ["alias", "als"];
+
+  void run() {
+    hasRun = true;
+  }
+}
+
+class AsyncCommand extends Command {
+  var hasRun = false;
+
+  final name = "async";
+  final description = "Set a value asynchronously.";
+  final takesArguments = false;
+
+  Future run() => new Future.value().then((_) => hasRun = true);
+}
 
 void throwsIllegalArg(function, {String reason: null}) {
   expect(function, throwsArgumentError, reason: reason);
 }
 
 void throwsFormat(ArgParser parser, List<String> args) {
   expect(() => parser.parse(args), throwsFormatException);
 }
+
+Matcher throwsUsageError(message, usage) {
+  return throwsA(predicate((error) {
+    expect(error, new isInstanceOf<UsageError>());
+    expect(error.message, message);
+    expect(error.usage, usage);
+    return true;
+  }));
+}