[pkg:observe] Add support for explicit change notification, even on dirty-checked objects

pkg/observe/test/observe_test.dart

 // Copyright (c) 2013, 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.
 
 import 'dart:async';
 import 'package:logging/logging.dart';
 import 'package:observe/observe.dart';
 import 'package:observe/src/dirty_check.dart' as dirty_check;
 import 'package:unittest/unittest.dart';
 import 'observe_test_utils.dart';
@@ skipping 175 matching lines @@
       runAsync(expectAsync0(() {
         subs.add(t.changes.listen(expectAsync1((records) {
           expectChanges(records, _changedValue(1));
         })));
         t.value = 777;
         runAsync(Observable.dirtyCheck);
       }));
     }));
     t.value = 42;
   });
+
+  observeTest('cannot modify changes list', () {
+    var t = createModel(123);
+    var records = null;
+    subs.add(t.changes.listen((r) { records = r; }));
+    t.value = 42;
+
+    performMicrotaskCheckpoint();
+    expectChanges(records, _changedValue(1));
+
+    // Verify that mutation operations on the list fail:
+
+    expect(() {
+      records[0] = new PropertyChangeRecord(_VALUE);
+    }, throwsUnsupportedError);
+
+    expect(() { records.clear(); }, throwsUnsupportedError);
+
+    expect(() { records.length = 0; }, throwsUnsupportedError);
+  });
+
+  observeTest('notifyChange', () {
+    var t = createModel(123);
+    var records = [];
+    subs.add(t.changes.listen((r) { records.addAll(r); }));
+    t.notifyChange(new PropertyChangeRecord(_VALUE));
+
+    performMicrotaskCheckpoint();
+    expectChanges(records, _changedValue(1));
+    expect(t.value, 123, reason: 'value did not actually change.');
+  });
+
+  observeTest('notifyPropertyChange', () {
+    var t = createModel(123);
+    var records = null;
+    subs.add(t.changes.listen((r) { records = r; }));
+    expect(t.notifyPropertyChange(_VALUE, t.value, 42), 42,
+        reason: 'notifyPropertyChange returns newValue');
+
+    performMicrotaskCheckpoint();
+    expectChanges(records, _changedValue(1));
+    expect(t.value, 123, reason: 'value did not actually change.');
+  });
 }
 
 _changedValue(len) => new List.filled(len, new PropertyChangeRecord(_VALUE));
 
 // A test model based on dirty checking.
 class WatcherModel<T> extends ObservableBase {
   @observable T value;
 
   WatcherModel([T initialValue]) : value = initialValue;
 
   String toString() => '#<$runtimeType value: $value>';
 }