Test breaks when using Future.delayed - dart

Question

I have used a Future.delayed to show a FAB in 1 second using this code:
Future.delayed(const Duration(seconds: 1), () {
setState(() {
_showFab = true;
});
});
Now the most basic smoke test has stopped working:
void main() {
testWidgets('smoke test', (WidgetTester tester) async {
await tester.pumpWidget(MyApp());
expect(find.byType(MyHomePage), findsOneWidget);
});
}
This is the error message:
══╡ EXCEPTION CAUGHT BY FLUTTER TEST FRAMEWORK ╞════════════════════════════════════════════════════
The following assertion was thrown running a test:
A Timer is still pending even after the widget tree was disposed.
'package:flutter_test/src/binding.dart': Failed assertion: line 933 pos 7:
'_currentFakeAsync.nonPeriodicTimerCount == 0' import 'dart:async';
Here is all the code used:
import 'package:flutter/material.dart';
import 'dart:async';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return MaterialApp(
home: MyHomePage(),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key}) : super(key: key);
#override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
bool _showFab = false;
#override
Widget build(BuildContext context) {
Future.delayed(const Duration(seconds: 1), () {
setState(() {
_showFab = true;
});
});
return Scaffold(
floatingActionButton: AnimatedOpacity(
opacity: _showFab ? 1.0 : 0.0,
duration: Duration(milliseconds: 1400),
child: FloatingActionButton(
onPressed: null,
child: Icon(Icons.add),
),
),
);
}
}
How can I change the unit test to make the test pass?

Answer 1

The test framework runs with FakeAsync by default, that has some limitations and might cause the error you get.
You can explicitly run with async proper like:
void main() {
testWidgets('smoke test', (WidgetTester tester) async {
await tester.runAsync(() async {
await tester.pumpWidget(MyApp());
expect(find.byType(MyHomePage), findsOneWidget);
});
});
}
You might still need suggestions made in other answers.

Answer 2

You need to give the tester enough time to process all the async calls you have scheduled, try change your smoke test to something like this:
void main() {
testWidgets('smoke test', (WidgetTester tester) async {
await tester.pumpWidget(MyApp());
// Since you wait 1 second to start the animation and another 1.4 to complete it
await tester.pump(Duration(seconds: 3));
expect(find.byType(MyHomePage), findsOneWidget);
});
}
You will also need to move the Future.delayed out of the build() method, because this is causing a cyclic behaviour, every time you call setState() the build() is called again, change your state like that:
class MyHomePage extends StatefulWidget {
MyHomePage({Key key}) : super(key: key);
#override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
bool _showFab = false;
#override
void initState() {
Future.delayed(const Duration(seconds: 1), () {
setState(() {
_showFab = true;
});
});
super.initState();
}
#override
Widget build(BuildContext context) {
return Scaffold(
floatingActionButton: AnimatedOpacity(
opacity: _showFab ? 1.0 : 0.0,
duration: Duration(milliseconds: 1400),
child: FloatingActionButton(
onPressed: null,
child: Icon(Icons.add),
),
),
);
}
}

Answer 3

You can wrap your Widget with TickerMode.
As you can see below:
void main() {
testWidgets('smoke test', (WidgetTester tester) async {
await tester.pumpWidget(TickerMode(child: MyApp(), enabled: false));
await tester.pumpAndSettle();
expect(find.byType(MyHomePage), findsOneWidget);
});
}

Answer 4

Try calling pumpAndSettle after you've pumped the widget. Like this:
void main() {
testWidgets('smoke test', (WidgetTester tester) async {
await tester.pumpWidget(MyApp());
await tester.pumpAndSettle();
expect(find.byType(MyHomePage), findsOneWidget);
});
}
From the docs
This essentially waits for all animations to have completed.

Answer 5

I tried using pump and pumpAndSettle but it didn't work. But add Duration in pumpAndSettle (not work for pump) makes it work again
await tester.pumpAndSettle(Duration(seconds: 1));