Add test of unittests.

tests/lib/mirrors/library_exports_shown_test.dart

 // Copyright (c) 2014, 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 test.library_imports;
+library test.library_exports_shown;
 
 import 'dart:mirrors';
 import 'package:expect/expect.dart';
 import 'stringify.dart';
 
 import 'library_exports_shown.dart';
 
 test(MirrorSystem mirrors) {
   LibraryMirror shown = mirrors.findLibrary(#library_exports_shown);
   LibraryMirror a = mirrors.findLibrary(#library_imports_a);
@@ skipping 10 matching lines @@
       ' show somethingFromA\n'
       ' show somethingFromBoth\n'
       'export library_imports_b\n'
       ' show somethingFromB\n',
       stringifyDependencies(shown));
 }
 
 main() {
   test(currentMirrorSystem());
 }