Fix widget tester

Author: Amar3tto

playground/frontend/playground_components_dev/lib/src/widget_tester.dart

@@ -161,13 +161,11 @@ extension WidgetTesterExtension on WidgetTester {
     expect(actualText, isNot(startsWith(kCachedResultsLog)));
     expectOutputIfDeployed(example, this);
 
-    // Animation stops just before the analytics event is fired, wait a bit.
-    await Future.delayed(const Duration(seconds: 1));
+    // Wait until the run is fully finished and analytics event is emitted.
+    final finishedEvent = await PlaygroundComponents.analyticsService.eventsStream
+        .whereType<RunFinishedAnalyticsEvent>()
+        .first;
 
-    final event = PlaygroundComponents.analyticsService.lastEvent;
-    expect(event, isA<RunFinishedAnalyticsEvent>());
-
-    final finishedEvent = event! as RunFinishedAnalyticsEvent;
     expect(finishedEvent.snippetContext, eventSnippetContext);
   }