Unit testing in Flutter - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the Flutter test package.

Flutter

import 'package:flutter_test/[1]';

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

Aflutter_test.dart

Bflutter

Ctest

Dflutter_test

Attempts:

3 left

💡 Hint

Common Mistakes

Adding '.dart' extension in the import path.

Using 'test' package instead of 'flutter_test'.

The correct import for Flutter's testing package is 'flutter_test' without any file extension.

2fill in blank

medium

Complete the code to define a test case with description 'adds two numbers'.

Flutter

test('[1]', () {
  expect(1 + 1, 2);
});

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

Aadds two numbers

Btest addition

Ccheck addition

Dsum test

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different test description string.

Omitting the test description.

The test description should be 'adds two numbers' as specified.

3fill in blank

hard

Fix the error in the test to correctly check if the result equals 5.

Flutter

test('check result', () {
  var result = 2 + 3;
  expect(result, [1]);
});

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

AisEqualTo(5)

Bequals(5)

C5

DequalTo(5)

Attempts:

3 left

💡 Hint

Common Mistakes

Using matcher functions like equals(5) which are not needed here.

Passing a string instead of a number.

The expect function compares the actual value to the expected value directly, so just use 5.

4fill in blank

hard

Fill both blanks to create a test group named 'Math tests' with a test inside it.

Flutter

group('[1]', () {
  test('[2]', () {
    expect(2 * 2, 4);
  });
});

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

AMath tests

BMultiplication test

CAddition test

DMath group

Attempts:

3 left

💡 Hint

Common Mistakes

Using unrelated group or test names.

Omitting the group or test description.

The group name is 'Math tests' and the test description is 'Multiplication test' as required.

5fill in blank

hard

Fill all three blanks to write a test that checks if a function 'add' returns 7 when adding 3 and 4.

Flutter

int [1](int a, int b) {
  return a + b;
}

test('[2]', () {
  expect([3](3, 4), 7);
});

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

Aadd

Badd function test

Dsum

Attempts:

3 left

💡 Hint

Common Mistakes

Mismatching function names in definition and call.

Using incorrect test description.

The function name is 'add', the test description is 'add function test', and the function call is 'add(3, 4)'.

Practice

1.

What is the main purpose of unit testing in Flutter?

easy

A. To check small parts of code for bugs early

B. To design the user interface

C. To deploy the app to the store

D. To write documentation for the app

Solution

1. Step 1: Understand unit testing purpose and compare options

   Unit testing focuses on testing small parts of code independently to find bugs early. Only To check small parts of code for bugs early matches the purpose of unit testing; others relate to different app development stages.

2. Final Answer:

   To check small parts of code for bugs early -> Option A

3. Quick Check:

   Unit testing = check small code parts early [OK]

Hint: Unit tests check small code parts, not UI or deployment [OK]

Common Mistakes:

• Confusing unit testing with UI design
• Thinking unit tests deploy the app
• Believing unit tests write documentation

2.

Which of the following is the correct syntax to write a simple test in Flutter?

?

easy

A. expect('description', test(() => 1 + 1 == 2));

B. test('description', () { expect(1 + 1, 2); });

C. test 'description' { expect(1 + 1 == 2); }

D. test(description, expect(1 + 1, 2));

Solution

1. Step 1: Recall Flutter test syntax and match options

   The correct syntax uses test('description', () { expect(actual, expected); }); Only test('description', () { expect(1 + 1, 2); }); matches the correct syntax with proper function and expect call.

2. Final Answer:

   test('description', () { expect(1 + 1, 2); }); -> Option B

3. Quick Check:

   Correct test syntax = test('description', () { expect(1 + 1, 2); }); [OK]

Hint: Remember test() takes a description and a function with expect() inside [OK]

Common Mistakes:

• Missing parentheses or curly braces
• Swapping test and expect arguments
• Using wrong function call syntax

3.

What will be the output of this test code?

int add(int a, int b) => a + b;

test('add function test', () {
  expect(add(2, 3), 5);
  expect(add(0, 0), 0);
  expect(add(-1, 1), 0);
});

Choose the correct test result.

medium

A. All tests fail

B. First test fails, others pass

C. Second test fails, others pass

D. All tests pass successfully

Solution

1. Step 1: Evaluate add function calls and check expect statements

   add(2, 3) = 5, add(0, 0) = 0, add(-1, 1) = 0, all match expected values. All expect statements compare actual and expected values correctly, so all pass.

2. Final Answer:

   All tests pass successfully -> Option D

3. Quick Check:

   Correct add results = all tests pass [OK]

Hint: Check function output matches expected values exactly [OK]

Common Mistakes:

• Assuming negative numbers cause failure
• Misreading expected values
• Ignoring zero as valid input

4.

Identify the error in this Flutter unit test code:

test('string length test', () {
  var str = 'hello';
  expect(str.length, '5');
});

medium

A. The test description is missing

B. The variable str is not defined

C. The expected value should be an integer, not a string

D. The expect function is used incorrectly

Solution

1. Step 1: Check expect arguments types and type mismatch effect

   str.length returns an integer (5), but expected value is a string ('5'). Expect compares values strictly, so integer 5 != string '5', causing test failure.

2. Final Answer:

   The expected value should be an integer, not a string -> Option C

3. Quick Check:

   Type mismatch in expect causes failure [OK]

Hint: Match expected value type exactly with actual value type [OK]

Common Mistakes:

• Using string instead of int for length
• Forgetting to define test description
• Misusing expect function parameters

5.

You want to test a function that returns a list of even numbers from a given list. Which test code correctly verifies this behavior?

List<int> filterEven(List<int> nums) => nums.where((n) => n % 2 == 0).toList();

// Which test is correct?

hard

A. test('filterEven test', () { expect(filterEven([1,2,3,4]), [2,4]); });

B. test('filterEven test', () { expect(filterEven([1,2,3,4]), [1,3]); });

C. test('filterEven test', () { expect(filterEven([1,2,3,4]), [2,3]); });

D. test('filterEven test', () { expect(filterEven([1,2,3,4]), [1,2,3,4]); });

Solution

1. Step 1: Understand filterEven function and check expected lists

   It returns a list of even numbers from input list. Only test('filterEven test', () { expect(filterEven([1,2,3,4]), [2,4]); }); expects the correct even numbers [2,4]. Others expect incorrect lists.

2. Final Answer:

   test('filterEven test', () { expect(filterEven([1,2,3,4]), [2,4]); }); -> Option A

3. Quick Check:

   Expected even numbers list = test('filterEven test', () { expect(filterEven([1,2,3,4]), [2,4]); }); [OK]

Hint: Expect only even numbers in the output list [OK]

Common Mistakes:

• Expecting odd numbers instead of even
• Including all numbers without filtering
• Mixing even and odd numbers in expected list