Minor fixes to support flutter/flutter tests.

packages/ui_primitives/lib/src/foundation/value_notifier.dart

@@ -396,14 +396,33 @@ class _ChangeNotifier implements Listenable {
 ///
 /// Because of this behavior, [ValueNotifier] is best used with immutable data
 /// types.
-interface class ValueNotifier<T> implements ValueListenable<T> {
+class ValueNotifier<T> implements ValueListenable<T> {
   final _ChangeNotifier _changeNotifier = _ChangeNotifier();
 
   /// Creates a [_ChangeNotifier] that wraps this value.
   ValueNotifier(this._value) {
-    if (kTrackMemoryLeaks) {
-      debugMaybeDispatchCreated(runtimeType.toString(), this);
-    }
+    assert(() {
+      if (kTrackMemoryLeaks) {
+        debugMaybeDispatchCreated(runtimeType.toString(), this);
+      }
+      return true;
+    }());
+  }
+
+  bool _debugDisposed = false;
+
+  static bool debugAssertNotDisposed<T>(ValueNotifier<T> notifier) {
+    assert(() {
+      if (notifier._debugDisposed) {
+        throw UiError(
+          'A ${notifier.runtimeType} was used after being disposed.\n'
+          'Once you have called dispose() on a ${notifier.runtimeType}, it '
+          'can no longer be used.',
+        );
+      }
+      return true;
+    }());
+    return true;
   }
 
   /// The current value stored in this notifier.
@@ -426,9 +445,12 @@ interface class ValueNotifier<T> implements ValueListenable<T> {
   String toString() => '${describeIdentity(this)}($value)';
 
   void dispose() {
-    if (kTrackMemoryLeaks) {
-      debugMaybeDispatchDisposed(this);
-    }
+    assert(() {
+      _debugDisposed = true;
+      if (kTrackMemoryLeaks) debugMaybeDispatchDisposed(this);
+      return true;
+    }());
+
     _changeNotifier.dispose();
   }
 
@@ -439,4 +461,10 @@ interface class ValueNotifier<T> implements ValueListenable<T> {
   @override
   void removeListener(VoidCallback listener) =>
       _changeNotifier.removeListener(listener);
+
+  @protected
+  bool get hasListeners => _changeNotifier.hasListeners;
+
+  @protected
+  void notifyListeners() => _changeNotifier.notifyListeners();
 }

packages/ui_primitives/pubspec.yaml

@@ -5,7 +5,7 @@
 name: ui_primitives
 description: Highly experimental package.
 repository: https://github.com/flutter/genui/tree/main/packages/ui_primitives
-version: 0.0.1-dev-003
+version: 0.0.1-dev-005
 
 resolution: workspace
 

packages/ui_primitives/test/smoke_test.dart

@@ -6,7 +6,7 @@ import 'package:test/test.dart';
 import 'package:ui_primitives/ui_primitives.dart';
 
 // ignore: unused_element, tests that ValueNotifier can be implemented.
-class _ValueNotifierOtherImplementaion<T> implements ValueNotifier<T> {
+class _ValueNotifierImplementaion<T> implements ValueNotifier<T> {
   @override
   void addListener(VoidCallback listener) {}
 
@@ -21,6 +21,17 @@ class _ValueNotifierOtherImplementaion<T> implements ValueNotifier<T> {
 
   @override
   set value(T newValue) {}
+
+  @override
+  bool get hasListeners => throw UnimplementedError();
+
+  @override
+  void notifyListeners() {}
+}
+
+// ignore: unused_element, tests that ValueNotifier can be extended.
+class _ValueNotifierExtention<T> extends ValueNotifier<T> {
+  _ValueNotifierExtention(super.value);
 }
 
 void main() {