Reorganize tests for samples so the test is discoverable from the sample

samples/swarm/test/swarm_ui_lib/observable/observable_test.dart

 // Copyright (c) 2011, 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 observable_tests;
 
 import 'dart:html';
-import '../../../../swarm/swarm_ui_lib/observable/observable.dart';
-import '../../../../../pkg/unittest/lib/unittest.dart';
-import '../../../../../pkg/unittest/lib/html_config.dart';
+import '../../../swarm_ui_lib/observable/observable.dart';
+import 'package:unittest/html_config.dart';
+import 'package:unittest/unittest.dart';
 
 part 'abstract_observable_tests.dart';
 part 'change_event_tests.dart';
 part 'event_batch_tests.dart';
 part 'observable_list_tests.dart';
 part 'observable_value_tests.dart';
 
 void main() {
   useHtmlConfiguration();
   group('AbstractObservable', testAbstractObservable);
@@ skipping 20 matching lines @@
   validateEvent(e, target, pName, index, ChangeEvent.INSERT, newVal, null);
 }
 
 void validateRemove(ChangeEvent e, target, pName, index, oldVal) {
   validateEvent(e, target, pName, index, ChangeEvent.REMOVE, null, oldVal);
 }
 
 void validateUpdate(ChangeEvent e, target, pName, index, newVal, oldVal) {
   validateEvent(e, target, pName, index, ChangeEvent.UPDATE, newVal, oldVal);
 }