Add File.modificationStamp accessor.

pkg/analyzer/test/file_system/memory_file_system_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.memory_file_system;
 
 import 'dart:async';
 
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/file_system/memory_file_system.dart';
 import 'package:analyzer/src/generated/engine.dart' show TimestampedData;
 import 'package:analyzer/src/generated/source.dart';
 import 'package:path/path.dart';
 import 'package:unittest/unittest.dart';
 import 'package:watcher/watcher.dart';
 
 
 var _isFile = new isInstanceOf<File>();
 var _isFolder = new isInstanceOf<Folder>();
-var _isMemoryResourceException = new isInstanceOf<MemoryResourceException>();
+var _isFileSystemException = new isInstanceOf<FileSystemException>();
 
 
 main() {
   groupSep = ' | ';
 
   group('MemoryResourceProvider', () {
     MemoryResourceProvider provider;
 
     setUp(() {
       provider = new MemoryResourceProvider();
     });
 
-    test('MemoryResourceException', () {
-      var exception = new MemoryResourceException('/my/path', 'my message');
+    test('FileSystemException', () {
+      var exception = new FileSystemException('/my/path', 'my message');
       expect(exception.path, '/my/path');
       expect(exception.message, 'my message');
       expect(
           exception.toString(),
-          'MemoryResourceException(path=/my/path; message=my message)');
+          'FileSystemException(path=/my/path; message=my message)');
     });
 
     group('Watch', () {
 
       Future delayed(computation()) {
         return new Future.delayed(Duration.ZERO, computation);
       }
 
       watchingFolder(String path, test(List<WatchEvent> changesReceived)) {
         Folder folder = provider.getResource(path);
@@ skipping 224 matching lines @@
         expect(file1.hashCode, equals(file2.hashCode));
       });
 
       test('isOrContains', () {
         String path = '/foo/bar/file.txt';
         File file = provider.getResource(path);
         expect(file.isOrContains(path), isTrue);
         expect(file.isOrContains('/foo/bar'), isFalse);
       });
 
+      group('modificationStamp', () {
+        test('exists', () {
+          String path = '/foo/bar/file.txt';
+          File file = provider.newFile(path, 'qwerty');
+          expect(file.modificationStamp, isNonNegative);
+        });
+
+        test('does not exist', () {
+          String path = '/foo/bar/file.txt';
+          File file = provider.newFile(path, 'qwerty');
+          provider.deleteFile(path);
+          expect(() {
+            file.modificationStamp;
+          }, throwsA(_isFileSystemException));
+        });
+      });
+
       test('shortName', () {
         File file = provider.getResource('/foo/bar/file.txt');
         expect(file.shortName, 'file.txt');
       });
 
       test('toString', () {
         File file = provider.getResource('/foo/bar/file.txt');
         expect(file.toString(), '/foo/bar/file.txt');
       });
 
@@ skipping 184 matching lines @@
 
       group('non-existent', () {
         setUp(() {
           File file = provider.getResource('/foo/test.dart');
           source = file.createSource();
         });
 
         test('contents', () {
           expect(() {
             source.contents;
-          }, throwsA(_isMemoryResourceException));
+          }, throwsA(_isFileSystemException));
         });
 
         test('encoding', () {
           expect(source.encoding, 'file:///foo/test.dart');
         });
 
         test('exists', () {
           expect(source.exists(), isFalse);
         });
 
         test('fullName', () {
           expect(source.fullName, '/foo/test.dart');
         });
 
+        test('modificationStamp', () {
+          expect(source.modificationStamp, -1);
+        });
+
         test('shortName', () {
           expect(source.shortName, 'test.dart');
         });
 
         test('resolveRelative', () {
           Uri relative =
               source.resolveRelativeUri(new Uri.file('bar/baz.dart'));
           expect(relative.path, '/foo/bar/baz.dart');
         });
       });
     });
   });
 }