Rename "tests" directories under /pkg to the singular "test"

pkg/unittest/tests/instance_test.dart

Index: pkg/unittest/tests/instance_test.dart
===================================================================
--- pkg/unittest/tests/instance_test.dart	(revision 10770)
+++ pkg/unittest/tests/instance_test.dart	(working copy)
@@ -1,29 +0,0 @@
-// 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('instance_test');
-#import('../../../pkg/unittest/unittest.dart');
-#source('test_utils.dart');
-
-doesThrow() { throw 'X'; }
-
-main() {
-  initUtils();
-
-  group('Type Matchers', () {
-    test('isInstanceOf', () {
-      shouldFail(0, new isInstanceOf<String>('String'),
-        "Expected: an instance of String but: was <0>.");
-      shouldPass('cow', new isInstanceOf<String>('String'));
-    });
-
-    test('throwsA', () {
-      shouldPass(doesThrow, throwsA(equals('X')));
-      shouldFail(doesThrow, throwsA(equals('Y')),
-        "Expected: throws an exception which matches 'Y' "
-        "but:  exception 'X' does not match 'Y'.");
-    });
-  });
-}
-