Wrap dart:io exception in getChildren(), implement for the memory FS.

pkg/analyzer/test/file_system/physical_resource_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 test.physical_file_system;
 
 import 'dart:async';
 import 'dart:io' as io;
 
 import 'package:analyzer/file_system/file_system.dart';
@@ skipping 294 matching lines @@
         });
 
         test('folder', () {
           new io.Directory(join(path, 'myFolder')).createSync();
           Folder child = folder.getChildAssumingFolder('myFolder');
           expect(child, isNotNull);
           expect(child.exists, isTrue);
         });
       });
 
-      test('getChildren', () {
-        // create 2 files and 1 folder
-        new io.File(join(path, 'a.txt')).createSync();
-        new io.Directory(join(path, 'bFolder')).createSync();
-        new io.File(join(path, 'c.txt')).createSync();
-        // prepare 3 children
-        List<Resource> children = folder.getChildren();
-        expect(children, hasLength(3));
-        children.sort((a, b) => a.shortName.compareTo(b.shortName));
-        // check that each child exists
-        children.forEach((child) {
-          expect(child.exists, true);
+      group('getChildren', () {
+        test('exists', () {
+          // create 2 files and 1 folder
+          new io.File(join(path, 'a.txt')).createSync();
+          new io.Directory(join(path, 'bFolder')).createSync();
+          new io.File(join(path, 'c.txt')).createSync();
+          // prepare 3 children
+          List<Resource> children = folder.getChildren();
+          expect(children, hasLength(3));
+          children.sort((a, b) => a.shortName.compareTo(b.shortName));
+          // check that each child exists
+          children.forEach((child) {
+            expect(child.exists, true);
+          });
+          // check names
+          expect(children[0].shortName, 'a.txt');
+          expect(children[1].shortName, 'bFolder');
+          expect(children[2].shortName, 'c.txt');
+          // check types
+          expect(children[0], _isFile);
+          expect(children[1], _isFolder);
+          expect(children[2], _isFile);
         });
-        // check names
-        expect(children[0].shortName, 'a.txt');
-        expect(children[1].shortName, 'bFolder');
-        expect(children[2].shortName, 'c.txt');
-        // check types
-        expect(children[0], _isFile);
-        expect(children[1], _isFolder);
-        expect(children[2], _isFile);
+
+        test('does not exist', () {
+          folder = folder.getChildAssumingFolder('no-such-folder');
+          expect(() {
+            folder.getChildren();
+          }, throwsA(_isFileSystemException));
+        });
       });
 
       test('parent', () {
         Resource parent = folder.parent;
         expect(parent, new isInstanceOf<Folder>());
         expect(parent.path, equals(tempPath));
 
         // Since the OS is in control of where tempPath is, we don't know how
         // far it should be from the root.  So just verify that each call to
         // parent results in a a folder with a shorter path, and that we
@@ skipping 18 matching lines @@
         expect(folder.canonicalizePath(join(path2, '..', 'folder3')),
             equals(path3));
         expect(folder.canonicalizePath(join('.', 'baz')),
             equals(join(path, 'baz')));
         expect(folder.canonicalizePath(join(path2, '.', 'baz')),
             equals(join(path2, 'baz')));
       });
     });
   });
 }