pkg/args: a bunch of test cleanup

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 'package:unittest/unittest.dart';
+import 'package:args/args.dart';
+
+void throwsIllegalArg(function, {String reason: null}) {
+  expect(function, throwsArgumentError, reason: reason);
+}
+
+void throwsFormat(ArgParser parser, List<String> args) {
+  expect(() => parser.parse(args), throwsFormatException);
+}