Dart Add Unit Test

Testing Dart and Flutter Applications

Contents

• Structuring Test Files
• Writing Tests
• Executing Tests
• Test Implementation Workflow
• Examples

Structuring Test Files

Organize test files to mirror the lib directory structure to maintain predictability.

• Place all test code within the test directory at the root of the package.
• Append _test.dart to the end of all test file names (e.g., lib/src/utils.dart should be tested in test/src/utils_test.dart).
• If writing integration tests, place them in an integration_test directory at the root of the package.

Writing Tests

Utilize package:test as the standard testing library for Dart applications.

• Import package:test/test.dart (or package:flutter_test/flutter_test.dart for Flutter).
• Group related tests using the group() function to provide shared context.
• Define individual test cases using the test() function.
• Validate outcomes using the expect() function alongside matchers (e.g., equals(), isTrue, throwsA()).
• Write asynchronous tests using standard async/await syntax. The test runner automatically waits for the Future to complete.
• Manage test setup and teardown using setUp() and tearDown() callbacks.
• If testing code that relies on dependency injection, use package:mockito alongside package:test to generate mock objects, configure fixed scenarios, and verify interactions.

Executing Tests

Select the appropriate test runner based on the project type and test location.

• If working on a pure Dart project, execute tests using the dart test command.
• If working on a Flutter project, execute tests using the flutter test command.
• If running integration tests, explicitly specify the directory path, as the default runner ignores it: dart test integration_test or flutter test integration_test.

Test Implementation Workflow

Follow this sequential workflow when implementing new test suites. Copy the checklist to track your progress.

Task Progress

• 1. Create the test file in the test/ directory, ensuring the _test.dart suffix.
• 2. Import package:test/test.dart and the target library.
• 3. Define a main() function.
• 4. Initialize shared resources or mocks using setUp().
• 5. Write test() cases grouped by functionality using group().
• 6. Execute the test suite using the appropriate CLI command.
• 7. Feedback Loop: Run test -> Review stack trace for failures -> Fix implementation or assertions -> Re-run until passing.

Examples

Standard Unit Test Suite

Demonstrates grouping, setup, synchronous, and asynchronous testing.

import 'package:test/test.dart';import 'package:my_package/calculator.dart';
void main() {  group('Calculator', () {    late Calculator calc;
    setUp(() {      calc = Calculator();    });
    test('adds two numbers correctly', () {      expect(calc.add(2, 3), equals(5));    });
    test('handles asynchronous operations', () async {      final result = await calc.fetchRemoteValue();      expect(result, isNotNull);      expect(result, greaterThan(0));    });  });}

Mocking with Mockito

Demonstrates configuring a mock object for dependency injection testing.

import 'package:test/test.dart';import 'package:mockito/mockito.dart';import 'package:mockito/annotations.dart';import 'package:my_package/api_client.dart';import 'package:my_package/data_service.dart';
// Generate the mock using build_runner: dart run build_runner build@GenerateNiceMocks([MockSpec<ApiClient>()])import 'data_service_test.mocks.dart';
void main() {  group('DataService', () {    late MockApiClient mockApiClient;    late DataService dataService;
    setUp(() {      mockApiClient = MockApiClient();      dataService = DataService(apiClient: mockApiClient);    });
    test('returns parsed data on successful API call', () async {      // Configure the mock      when(mockApiClient.get('/data')).thenAnswer((_) async => '{"id": 1}');
      // Execute the system under test      final result = await dataService.fetchData();
      // Verify outcomes and interactions      expect(result.id, equals(1));      verify(mockApiClient.get('/data')).called(1);    });  });}