nav test: Make TestNavigatorObserver extend TransitionDurationObserver

This way, we can use the instance of TestNavigatorObserver to wait for
the route transition to complete, instead of creating a different object
of TransitionDurationObserver for the same purpose.

Author: sm-sayedi

test/test_navigation.dart

@@ -1,11 +1,12 @@
 import 'package:flutter/widgets.dart';
+import 'package:flutter_test/flutter_test.dart';
 
 // Inspired by test code in the Flutter tree:
 //   https://github.com/flutter/flutter/blob/53082f65b/packages/flutter/test/widgets/observer_tester.dart
 //   https://github.com/flutter/flutter/blob/53082f65b/packages/flutter/test/widgets/navigator_test.dart
 
 /// A trivial observer for testing the navigator.
-class TestNavigatorObserver extends NavigatorObserver {
+class TestNavigatorObserver extends TransitionDurationObserver{
   void Function(Route<dynamic> topRoute, Route<dynamic>? previousTopRoute)? onChangedTop;
   void Function(Route<dynamic> route, Route<dynamic>? previousRoute)? onPushed;
   void Function(Route<dynamic> route, Route<dynamic>? previousRoute)? onPopped;
@@ -21,11 +22,13 @@ class TestNavigatorObserver extends NavigatorObserver {
 
   @override
   void didPush(Route<dynamic> route, Route<dynamic>? previousRoute) {
+    super.didPush(route, previousRoute);
     onPushed?.call(route, previousRoute);
   }
 
   @override
   void didPop(Route<dynamic> route, Route<dynamic>? previousRoute) {
+    super.didPop(route, previousRoute);
     onPopped?.call(route, previousRoute);
   }
 
@@ -36,6 +39,7 @@ class TestNavigatorObserver extends NavigatorObserver {
 
   @override
   void didReplace({ Route<dynamic>? oldRoute, Route<dynamic>? newRoute }) {
+    super.didReplace();
     onReplaced?.call(newRoute, oldRoute);
   }