Make mappedBy lazy.

utils/tests/archive/reader_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 reader_test;
 
 import 'dart:io';
 import '../../../pkg/unittest/lib/unittest.dart'
 import '../../archive/archive.dart';
 
@@ skipping 39 matching lines @@
   });
 
   test('reading a .tar.gz file with readAll', () {
     var reader = new ArchiveReader();
     reader.format.tar = true;
     reader.filter.gzip = true;
 
     var future = reader.openFilename("$dataPath/test-archive.tar.gz")
       .chain((input) => input.readAll())
       .transform((entries) {
-      entries = entries.mappedBy((entry) => [entry.pathname, entry.contents.trim()]);
+      entries = entries
+          .mappedBy((entry) => [entry.pathname, entry.contents.trim()])
+          .toList();
       expect(entries[0], orderedEquals(["filename1", "contents 1"]));
       expect(entries[1], orderedEquals(["filename2", "contents 2"]));
       expect(entries[2], orderedEquals(["filename3", "contents 3"]));
     });
 
     expect(future, completes);
   });
 
   test('reading an in-memory .tar.gz', () {
     var asyncDone = expectAsync0(() {});
@@ skipping 118 matching lines @@
   test("opening a non-existent archive", () {
     var reader = new ArchiveReader();
     reader.format.tar = true;
     reader.filter.gzip = true;
 
     expect(reader.openFilename("$dataPath/non-existent.tar.gz"),
       throwsA((e) => e is ArchiveException));
   });
 }