Get codebase ready for actually supporting versioning.

utils/tests/pub/pubspec_test.dart

+// Copyright (c) 2012, 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('source_test');
+
+#import('../../../lib/unittest/unittest.dart');
+#import('../../pub/pubspec.dart');
+#import('../../pub/source.dart');
+#import('../../pub/utils.dart');
+
+class MockSource extends Source {
+  final String name = "mock";
+  final bool shouldCache = false;
+  void validateDescription(description) {
+    if (description != 'ok') throw new FormatException('Bad');
+  }
+}
+
+main() {
+  group('Pubspec', () {
+    group('parse()', () {
+      test("throws if the description isn't valid", () {
+        var sources = new SourceRegistry();
+        sources.register(new MockSource());
+
+        throwsBadFormat(() {
+        new Pubspec.parse('''
+dependencies:
+  foo:
+    mock: bad
+''', sources);
+        });
+      });
+    });
+  });
+}
+
+throwsBadFormat(function) {
+  expectThrow(function, (e) => e is FormatException);
+}