MemoryResourceProvider.getFolder() should not create the folder.

pkg/analyzer/test/source/package_map_provider_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 analyzer.test.source.package_map_provider_test;
 
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/file_system/memory_file_system.dart';
 import 'package:analyzer/source/package_map_provider.dart';
 import 'package:analyzer/source/pub_package_map_provider.dart';
@@ skipping 15 matching lines @@
   PubPackageMapProvider packageMapProvider;
   String projectPath;
   Folder projectFolder;
 
   PackageMapInfo parsePackageMap(Map obj) {
     return packageMapProvider.parsePackageMap(obj, projectFolder);
   }
 
   void setUp() {
     resourceProvider = new MemoryResourceProvider();
-    sdk = new FolderBasedDartSdk(resourceProvider,
-        FolderBasedDartSdk.defaultSdkDirectory(resourceProvider));
+    Folder sdkFolder = resourceProvider
+        .newFolder(resourceProvider.convertPath('/Users/user/dart-sdk'));
+    sdk = new FolderBasedDartSdk(resourceProvider, sdkFolder);
     packageMapProvider = new PubPackageMapProvider(resourceProvider, sdk);
     projectPath = resourceProvider.convertPath('/path/to/project');
     projectFolder = resourceProvider.newFolder(projectPath);
   }
 
   void test_computePackageMap_noLockFile() {
     packageMapProvider =
         new PubPackageMapProvider(resourceProvider, sdk, (Folder folder) {
       fail('Unexpected "pub list" invocation');
     });
@@ skipping 89 matching lines @@
     resourceProvider.newFolder(projectPath);
     resourceProvider.newFile(dependencyPath, 'contents');
     Set<String> dependencies = parsePackageMap({
       'packages': {},
       'input_files': [relativeDependencyPath]
     }).dependencies;
     expect(dependencies, hasLength(1));
     expect(dependencies, contains(dependencyPath));
   }
 }