Test coverage in Flutter - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ ui_behavior

intermediate

What is the output of this Flutter widget test?

Consider this Flutter widget test code. What will the test find when it runs?

Flutter

testWidgets('Finds a Text widget with Hello', (WidgetTester tester) async {
  await tester.pumpWidget(MaterialApp(home: Scaffold(body: Text('Hello'))));
  final textFinder = find.text('Hello');
  expect(textFinder, findsOneWidget);
});

A The test fails because the Text widget is not found.

B The test passes because the Text widget with 'Hello' is found exactly once.

C The test fails because there are multiple Text widgets with 'Hello'.

D The test throws a runtime error due to missing MaterialApp.

💡 Hint

Remember that MaterialApp provides necessary context for Text widgets.

The test pumps a MaterialApp with a Scaffold containing a Text widget with 'Hello'. The find.text('Hello') finds exactly one widget, so the expect passes.

❓ lifecycle

intermediate

What is the value of counter after this test runs?

Given this Flutter widget test that increments a counter, what is the final value of counter?

Flutter

int counter = 0;

class CounterButton extends StatelessWidget {
  final VoidCallback onPressed;
  CounterButton({required this.onPressed});

  @override
  Widget build(BuildContext context) {
    return ElevatedButton(onPressed: onPressed, child: Text('Increment'));
  }
}

testWidgets('Counter increments on button tap', (WidgetTester tester) async {
  await tester.pumpWidget(MaterialApp(home: CounterButton(onPressed: () { counter++; })));
  await tester.tap(find.byType(ElevatedButton));
  await tester.pump();
});

A counter is 1 after the test runs.

B counter is 0 because the button was not tapped.

C counter is 2 because the button was tapped twice.

D counter is null due to uninitialized variable.

💡 Hint

Check how many times tester.tap is called.

The test taps the ElevatedButton once, triggering the onPressed callback which increments counter from 0 to 1.

📝 Syntax

advanced

What error does this Flutter test code produce?

Analyze this Flutter test code snippet. What error will it cause when run?

Flutter

testWidgets('Missing await on pumpWidget', (WidgetTester tester) {
  tester.pumpWidget(MaterialApp(home: Text('Test')));
  final textFinder = find.text('Test');
  expect(textFinder, findsOneWidget);
});

A No error; test passes successfully.

B Test fails with a MissingPluginException error.

C Test fails because pumpWidget is not awaited, causing a test failure.

D Test fails with a syntax error due to missing semicolon.

💡 Hint

pumpWidget returns a Future and should be awaited in async tests.

The testWidgets callback is not marked async and pumpWidget is not awaited, so the widget tree is not built before the find and expect calls, causing the test to fail.

🔧 Debug

advanced

Why does this widget test fail to find the button?

This test tries to find a button but fails. What is the cause?

Flutter

testWidgets('Finds button by key', (WidgetTester tester) async {
  await tester.pumpWidget(MaterialApp(home: Scaffold(body: ElevatedButton(key: Key('btn'), onPressed: () {}, child: Text('Tap me')))));
  final buttonFinder = find.byKey(Key('button'));
  expect(buttonFinder, findsOneWidget);
});

A The key used in find.byKey does not match the button's key.

B The ElevatedButton is not wrapped in a MaterialApp.

C The test does not await tester.pumpWidget.

D The button's child Text widget is missing.

💡 Hint

Check the key strings used in the widget and the finder.

The button's key is 'btn' but the finder looks for key 'button', so it does not find the widget.

🧠 Conceptual

expert

Which option best describes test coverage in Flutter?

Select the statement that correctly explains test coverage in Flutter development.

A Test coverage refers to the number of devices a Flutter app supports.

B Test coverage is the time taken to run all tests in a Flutter project.

C Test coverage is the number of UI widgets visible on the screen during testing.

D Test coverage measures the percentage of code executed by automated tests, helping identify untested parts.

💡 Hint

Think about what 'coverage' means in software testing.

Test coverage shows how much of the app's code is tested by automated tests, helping developers find untested code.