Flutter widget test of a custom widget fails - dart

Question

I am trying to test a custom widget GoogleSignInButton.
Here is the implementation of the widget:
import 'package:flutter/material.dart';
class GoogleSignInButton extends StatelessWidget {
GoogleSignInButton({this.onPressed});
final Function onPressed;
#override
Widget build(BuildContext context) {
Image _buildLogo() {
return Image.asset(
"assets/g-logo.png",
height: 18.0,
width: 18.0,
);
}
Opacity _buildText() {
return Opacity(
opacity: 0.54,
child: Text(
"Sign in with Google",
style: TextStyle(
fontFamily: 'Roboto-Medium',
color: Colors.black,
),
),
);
}
return MaterialButton(
height: 40.0,
onPressed: this.onPressed,
color: Colors.white,
child: Row(
mainAxisSize: MainAxisSize.min,
children: <Widget>[
_buildLogo(),
SizedBox(width: 24.0),
_buildText(),
],
),
);
}
}
I am trying to test the onPressed function callback by the test that follows.
import 'package:flutter/material.dart';
import 'package:flutter_test/flutter_test.dart';
import '../lib/ui/widgets/google_sign_in_button.dart';
void main() {
testWidgets('my first widget test', (WidgetTester tester) async {
var pressed = false;
var widget = GoogleSignInButton(
onPressed: () => () {
pressed = true;
},
);
await tester.pumpWidget(
StatefulBuilder(
builder: (BuildContext context, StateSetter setState) {
return MaterialApp(
home: Material(
child: Center(
child: widget,
),
),
);
},
),
);
await tester.press(find.byWidget(widget));
expect(pressed, equals(true));
});
}
Unfortunately, the test fails.
I am executing my widget test on the command line by flutter test test/widget_test.dart and here is the result of the test:
══╡ EXCEPTION CAUGHT BY FLUTTER TEST FRAMEWORK ╞════════════════════════════════════════════════════
The following TestFailure object was thrown running a test:
Expected: <true>
Actual: <false>
When the exception was thrown, this was the stack:
#4 main.<anonymous closure> (file:///home/hans/Development/flutter/recipes_app/test/widget_test.dart:30:5)
<asynchronous suspension>
#5 testWidgets.<anonymous closure>.<anonymous closure> (package:flutter_test/src/widget_tester.dart:72:23)
#6 TestWidgetsFlutterBinding._runTestBody (package:flutter_test/src/binding.dart:566:19)
<asynchronous suspension>
#9 TestWidgetsFlutterBinding._runTest (package:flutter_test/src/binding.dart:550:14)
#10 AutomatedTestWidgetsFlutterBinding.runTest.<anonymous closure> (package:flutter_test/src/binding.dart:893:24)
#16 AutomatedTestWidgetsFlutterBinding.runTest (package:flutter_test/src/binding.dart:890:15)
#17 testWidgets.<anonymous closure> (package:flutter_test/src/widget_tester.dart:71:22)
#18 Declarer.test.<anonymous closure>.<anonymous closure>.<anonymous closure> (package:test_api/src/backend/declarer.dart:168:27)
<asynchronous suspension>
#19 Invoker.waitForOutstandingCallbacks.<anonymous closure> (package:test_api/src/backend/invoker.dart:249:15)
<asynchronous suspension>
#24 Invoker.waitForOutstandingCallbacks (package:test_api/src/backend/invoker.dart:246:5)
#25 Declarer.test.<anonymous closure>.<anonymous closure> (package:test_api/src/backend/declarer.dart:166:33)
#30 Declarer.test.<anonymous closure> (package:test_api/src/backend/declarer.dart:165:13)
<asynchronous suspension>
#31 Invoker._onRun.<anonymous closure>.<anonymous closure>.<anonymous closure>.<anonymous closure> (package:test_api/src/backend/invoker.dart:399:25)
<asynchronous suspension>
#45 _Timer._runTimers (dart:isolate/runtime/libtimer_impl.dart:382:19)
#46 _Timer._handleMessage (dart:isolate/runtime/libtimer_impl.dart:416:5)
#47 _RawReceivePortImpl._handleMessage (dart:isolate/runtime/libisolate_patch.dart:171:12)
(elided 28 frames from class _FakeAsync, package dart:async, and package stack_trace)
This was caught by the test expectation on the following line:
file:///home/hans/Development/flutter/recipes_app/test/widget_test.dart line 30
The test description was:
my first widget test
════════════════════════════════════════════════════════════════════════════════════════════════════
00:01 +0 -1: my first widget test [E]
Test failed. See exception logs above.
The test description was: my first widget test
00:02 +0 -1: Some tests failed.
Any ideas why the test fails?

Answer 1

Your closure is wrong:
() => () {
pressed = true;
},
You need to write it either like that
() {
pressed = true;
},
Or like that
() => ( pressed = true )
And you need to trigger the tester.tap method.
That's my working code:
var pressed = false;
var widget = GoogleSignInButton(
onPressed: () {
pressed = true;
debugPrint("Pressed!");
},
);
await tester.pumpWidget(
StatefulBuilder(
builder: (BuildContext context, StateSetter setState) {
return MaterialApp(
home: Material(
child: Center(
child: widget,
),
),
);
},
),
);
expect(find.byWidget(widget), findsOneWidget);
await tester.tap(find.byWidget(widget));
expect(pressed, isTrue);
And I've supposed that when you run your project your Widget renders well and does not throw any errors.
HINT: make a flutter clean after any change in your test_file.dart change.