Cookbooks
Dart
Chapter 9. Testing and Debugging
Writing tests

Dart:
Writing tests

How to:

In Dart, the test package is commonly used for writing tests. First, add the test package to your pubspec.yaml:

dev_dependencies:
  test: ^1.0.0

Then, write a test for a simple function. Suppose you have a function that adds two numbers:

int add(int a, int b) {
  return a + b;
}

Next, create a file named add_test.dart in the test directory and write your test case:

import 'package:test/test.dart';
import '../lib/add.dart'; // Assume your `add` function is in lib/add.dart

void main() {
  test('adds two numbers', () {
    var expected = 3;
    expect(add(1, 2), equals(expected));
  });
}

To run the tests, use the Dart command:

$ dart test

Sample output might resemble:

00:01 +1: All tests passed!

Using a third-party library: Mockito for mocking

For testing code that has complex dependencies, you might use Mockito to create mock objects. First, add Mockito to your pubspec.yaml:

dev_dependencies:
  mockito: ^5.0.0

Assuming you have a class UserRepository that fetches user data, and you want to test a UserService that depends on UserRepository without hitting a real database:

import 'package:mockito/mockito.dart';
import 'package:test/test.dart';
import 'package:your_project/user_repository.dart';
import 'package:your_project/user_service.dart';

// Create a Mock class using Mockito
class MockUserRepository extends Mock implements UserRepository {}

void main() {
  group('UserService Tests', () {
    test('Fetches user successfully', () {
      // Create mock instance
      final mockUserRepository = MockUserRepository();
      final userService = UserService(mockUserRepository);

      // Setting up mock behavior
      when(mockUserRepository.fetchUser(1)).thenReturn(User(id: 1, name: 'Test User'));

      // Asserting that the mocked method is called with expected arguments
      expect(userService.getUserName(1), 'Test User');
      verify(mockUserRepository.fetchUser(1)).called(1);
    });
  });
}

Running this test confirms that UserService correctly interacts with UserRepository, using mocking to simulate the real interactions in a controlled way.

Using a debugger