Test coverage in Flutter - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the Flutter test package needed for writing tests.

Flutter

import '[1]';

void main() {
  test('Simple test', () {
    expect(1 + 1, 2);
  });
}

Drag options to blanks, or click blank then click option'

Apackage:flutter/widgets.dart

Bpackage:flutter/material.dart

Cpackage:flutter_test/flutter_test.dart

Dpackage:flutter/src/widgets/framework.dart

Attempts:

3 left

💡 Hint

Common Mistakes

Importing material.dart instead of flutter_test.dart

Forgetting to import any test package

The correct import for Flutter testing utilities is 'package:flutter_test/flutter_test.dart'.

2fill in blank

medium

Complete the code to define a widget test that checks if a Text widget displays the correct string.

Flutter

testWidgets('Check Text widget', (WidgetTester [1]) async {
  await tester.pumpWidget(const Text('Hello'));
  expect(find.text('Hello'), findsOneWidget);
});

Drag options to blanks, or click blank then click option'

Atester

Bwidget

Ccontext

DtesterWidget

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect parameter names like 'widget' or 'context'

Not using the WidgetTester parameter at all

The testWidgets function provides a WidgetTester object usually named 'tester' to interact with widgets.

3fill in blank

hard

Fix the error in the test code by completing the missing method to rebuild the widget tree after state changes.

Flutter

testWidgets('Tap button increments counter', (WidgetTester tester) async {
  await tester.pumpWidget(const MyCounterApp());
  await tester.tap(find.byIcon(Icons.add));
  await tester.[1]();
  expect(find.text('1'), findsOneWidget);
});

Drag options to blanks, or click blank then click option'

Apump

Btap

Cbuild

Drebuild

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'tap()' again instead of 'pump()'

Using non-existent methods like 'rebuild()'

After simulating a tap, calling 'pump()' rebuilds the widget tree to reflect changes.

4fill in blank

hard

Fill both blanks to create a test that verifies a widget is not found after an action.

Flutter

testWidgets('Verify widget disappears', (WidgetTester tester) async {
  await tester.pumpWidget(const MyWidget());
  await tester.tap(find.byKey(Key('removeButton')));
  await tester.[1]();
  expect(find.byType(Text), [2]);
});

Drag options to blanks, or click blank then click option'

Apump

BfindsNothing

CfindsOneWidget

Dtap

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'tap()' instead of 'pump()' after interaction

Using 'findsOneWidget' when expecting no widget

After tapping, 'pump()' rebuilds the UI, and 'findsNothing' checks that the widget is gone.

5fill in blank

hard

Fill all three blanks to write a test that pumps a widget, taps a button, and verifies the counter text updates.

Flutter

testWidgets('Counter increments test', (WidgetTester [1]) async {
  await [1].pumpWidget(const CounterApp());
  await [1].tap(find.byIcon(Icons.add));
  await [1].[2]();
  expect(find.text('[3]'), findsOneWidget);
});

Drag options to blanks, or click blank then click option'

Atester

Bpump

C1

Dtap

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong variable names instead of 'tester'

Forgetting to call 'pump()' after tap

Checking wrong text value

The WidgetTester is named 'tester'. After tapping, call 'pump()' to rebuild. The counter text should show '1'.

Practice

1.

What does test coverage measure in a Flutter app?

easy

A. How much of the app's code is executed by tests

B. The number of tests written

C. The speed of test execution

D. The size of the app's binary

Solution

1. Step 1: Understand test coverage meaning

   Test coverage shows what percentage of your code runs when tests are executed.

2. Step 2: Compare options to definition

   Only How much of the app's code is executed by tests matches this meaning by describing code executed by tests.

3. Final Answer:

   How much of the app's code is executed by tests -> Option A

4. Quick Check:

   Test coverage = code executed by tests [OK]

Hint: Coverage means code tested, not test count or speed [OK]

Common Mistakes:

• Confusing coverage with number of tests
• Thinking coverage measures test speed
• Assuming coverage relates to app size

2.

Which command runs Flutter tests and collects coverage data?

?

easy

A. flutter test --coverage

B. flutter run --coverage

C. flutter build --coverage

D. flutter analyze --coverage

Solution

1. Step 1: Recall Flutter test commands

   The command to run tests and collect coverage is flutter test --coverage.

2. Step 2: Eliminate incorrect commands

   flutter run runs the app, flutter build builds it, and flutter analyze checks code style, none collect coverage.

3. Final Answer:

   flutter test --coverage -> Option A

4. Quick Check:

   Run tests with coverage = flutter test --coverage [OK]

Hint: Use flutter test --coverage to get coverage data [OK]

Common Mistakes:

• Using flutter run instead of flutter test
• Confusing build or analyze commands with testing
• Omitting the --coverage flag

3.

Given this test code snippet, what is the coverage result for increment() method?

class Counter {
  int value = 0;
  void increment() {
    value++;
  }
}

void main() {
  final counter = Counter();
  test('value starts at 0', () {
    expect(counter.value, 0);
  });
}

medium

A. 100% coverage including increment()

B. Partial coverage of increment() method

C. 0% coverage for increment() method

D. Syntax error prevents coverage

Solution

1. Step 1: Analyze test coverage of increment()

   The test only checks initial value; it never calls increment().

2. Step 2: Determine coverage for increment()

   Since increment() is never executed, coverage for it is 0%.

3. Final Answer:

   0% coverage for increment() method -> Option C

4. Quick Check:

   Method not called = 0% coverage [OK]

Hint: Only called code counts as covered [OK]

Common Mistakes:

• Assuming all methods are covered by default
• Confusing test presence with code execution
• Ignoring that increment() is never called

4.

Identify the error in this test setup that causes coverage to be incomplete:

void main() {
  final counter = Counter();
  test('increment test', () {
    counter.increment;
    expect(counter.value, 1);
  });
}

medium

A. Test name is missing

B. Missing parentheses to call increment() method

C. expect() syntax is incorrect

D. Counter class is not imported

Solution

1. Step 1: Check method call syntax

   The code uses counter.increment; which references the method but does not call it.

2. Step 2: Understand impact on coverage

   Because increment() is not called, coverage misses this method.

3. Final Answer:

   Missing parentheses to call increment() method -> Option B

4. Quick Check:

   Method call needs () to execute [OK]

Hint: Method calls need () to run and count for coverage [OK]

Common Mistakes:

• Forgetting () after method name
• Assuming method reference calls it
• Ignoring test name importance (not required)

5.

You want to improve test coverage for this class. Which test addition best increases coverage?

class Calculator {
  int add(int a, int b) => a + b;
  int subtract(int a, int b) => a - b;
  int multiply(int a, int b) => a * b;
}

Current tests only call add().

hard

A. Add tests checking only Calculator class existence

B. Add tests calling add() multiple times

C. Add tests that print results without assertions

D. Add tests calling subtract() and multiply() methods

Solution

1. Step 1: Identify untested methods

   Only add() is tested; subtract() and multiply() are not covered.

2. Step 2: Add tests for untested methods

   Writing tests that call subtract() and multiply() will increase coverage.

3. Final Answer:

   Add tests calling subtract() and multiply() methods -> Option D

4. Quick Check:

   Test all methods to increase coverage [OK]

Hint: Test all methods, not just one, to boost coverage [OK]

Common Mistakes:

• Testing only one method repeatedly
• Testing class existence without method calls
• Printing results without assertions doesn't count