Properly use the sandbox in tag_test.dart.

test/runner/tag_test.dart

 // Copyright (c) 2015, 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.
 
 @TestOn("vm")
 
 import 'package:scheduled_test/descriptor.dart' as d;
 import 'package:scheduled_test/scheduled_stream.dart';
 import 'package:scheduled_test/scheduled_test.dart';
 
 import '../io.dart';
 
 void main() {
-  useSandbox();
-
-  setUp(() {
+  useSandbox(() {
     d.file("test.dart", """
       import 'package:test/test.dart';
 
       void main() {
         test("no tags", () {});
         test("a", () {}, tags: "a");
         test("b", () {}, tags: "b");
         test("bc", () {}, tags: ["b", "c"]);
       }
     """).create();
@@ skipping 308 matching lines @@
   }
 
   // Consume until the end of the warning block, and assert that it has no
   // further tags than the ones we specified.
   yield consumeWhile(isNot(anyOf([contains(" was used in"), isEmpty])));
   yield isEmpty;
 }());
 
 /// Returns a [StreamMatcher] that matches the lines of [string] in order.
 StreamMatcher lines(String string) => inOrder(string.split("\n"));