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Lesson 24 min

Unit Testing in Dart

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Unit Testing in Dart

Testing is a critical part of professional software development. Writing tests ensures that your code works as expected today, and continues to work as expected as you add new features or refactor existing code.

In this lesson, we will cover how to write unit tests using Dart's official test package.

1. Setting Up the Test Environment

To write tests, you need to add the test package to your dev_dependencies inside your pubspec.yaml file.

yaml
name: my_dart_project
description: A sample command-line application.
version: 1.0.0

environment:
  sdk: '>=3.0.0 <4.0.0'

dependencies:
  # App dependencies go here

dev_dependencies:
  test: ^1.24.0

Run dart pub get to download and install the package.

2. Writing Your First Test

By convention, all test files must:

  • Be located inside a top-level directory named test/.
  • End with the suffix _test.dart (e.g., calculator_test.dart).

Here is a simple calculator class and its corresponding unit test:

Implementation: lib/calculator.dart

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

Test File: test/calculator_test.dart

dart
import 'package:test/test.dart';
import 'package:my_dart_project/calculator.dart';

void main() {
  group('Calculator Tests', () {
    final calculator = Calculator();

    test('Addition should return the sum of two integers', () {
      final result = calculator.add(10, 5);
      expect(result, equals(15));
    });

    test('Subtraction should return the difference of two integers', () {
      final result = calculator.subtract(10, 5);
      expect(result, equals(5));
    });
  });
}

3. Key Testing Functions

group()

Used to group related tests together. This helps organize output logs and makes it easy to apply common setup logic to a batch of tests.

test()

Defines a single test case. It takes a description string and an execution body.

expect()

An assertion check. It compares the actual value returned by your code against the expected matcher value.

4. Lifecycle Hooks: Setup and Teardown

If your tests require setting up database connections, creating mock profiles, or cleaning up filesystem changes, use Dart's lifecycle hooks:

  • setUp(): Runs a block of code before every test in the group.
  • tearDown(): Runs a block of code after every test in the group.
  • setUpAll(): Runs once before any tests in the group start.
  • tearDownAll(): Runs once after all tests in the group complete.
dart
void main() {
  late DatabaseConnection db;

  setUp(() {
    db = DatabaseConnection();
    db.open();
  });

  tearDown(() {
    db.close();
  });

  test('Query user returns valid profile', () {
    var user = db.getUser(1);
    expect(user.name, equals("Admin"));
  });
}

5. Running Your Tests

Run the test suite from your terminal:

bash
# Run all tests in the project
dart test

# Run a specific test file
dart test test/calculator_test.dart

Summary

  • Unit tests verify the smallest testable parts (methods/functions) of your application.
  • Put all tests in the test/ directory, naming files with the _test.dart suffix.
  • Use group() to organize tests, test() to define cases, and expect() with matchers to assert results.
  • Leverage setUp() and tearDown() lifecycle hooks to manage test state.
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