单元测试与模拟
为 Flutter 业务逻辑编写快速、隔离的单元测试，并使用模拟对象测试依赖服务和 API 的代码。
单元测试与模拟 是 CoddyKit 上的免费 Flutter Mobile Development 课时。 这是第 4 节课，共 4 节。 你可以在下方免费阅读本课时的完整内容 — 然后在浏览器中使用内置代码编辑器和全天候 AI 导师进行实践。 这是 Flutter Mobile Development 学习路径的一部分，你的进度在网页和 CoddyKit 应用中同步。 Flutter Mobile Development 课程共包含 4 节课。
本课时的部分内容尚未翻译，以英文显示。
The Testing Pyramid
You have seen widget and integration tests. At the base sits the fastest layer: unit tests that verify a single function or class in isolation.
- Many unit tests (fast)
- Fewer widget tests
- Even fewer integration tests (slow)
Anatomy of a Unit Test
A unit test uses test() and expect() from the test package.
import 'package:test/test.dart';
void main() {
test('adds two numbers', () {
expect(2 + 3, equals(5));
});
}Testing a Class
Instantiate the class under test and assert on its behaviour.
test('counter increments', () {
final counter = Counter();
counter.increment();
expect(counter.value, 1);
});Matchers
Matchers express expectations clearly.
equals(x)isTrue/isNullthrowsExceptioncontains(x)
expect(list, contains('apple'));
expect(() => parse('bad'), throwsFormatException);Grouping Tests
Use group() to organize related tests and share setup.
group('Cart', () {
test('starts empty', () { ... });
test('adds items', () { ... });
});setUp & tearDown
setUp runs before each test; tearDown runs after — perfect for fresh fixtures.
late Cart cart;
setUp(() => cart = Cart());
tearDown(() => cart.clear());The Problem of Dependencies
What if your class calls a real API or database? Tests would be slow and flaky. The solution is mocking — replacing dependencies with fakes you control.
Mockito Setup
Add mockito and build_runner, then annotate to generate mocks.
@GenerateMocks([ApiService])
void main() {}
// flutter pub run build_runner buildStubbing Methods
Use when(...).thenReturn(...) to define what a mock returns.
final mockApi = MockApiService();
when(mockApi.fetchUser()).thenAnswer((_) async => User('Ada'));Verifying Interactions
verify confirms a method was called the expected number of times.
await repository.loadUser();
verify(mockApi.fetchUser()).called(1);Testing Async Code
Mark the test body async and await futures, or use the completes matcher.
test('loads data', () async {
final result = await repo.load();
expect(result, isNotEmpty);
});Quick Check
Why would you use a mock in a unit test?
Recap
You learned unit testing and mocking:
- test/expect/matchers and group/setUp
- Mockito to generate mocks
- when().thenReturn and verify().called
- Testing async code
Unit tests give you fast confidence in your business logic.
常见问题解答
「单元测试与模拟」课时是免费的吗？
是的 — 「单元测试与模拟」的完整文本可在网页上免费阅读。要进行交互式练习（内置代码编辑器和全天候 AI 导师）并解锁 Flutter Mobile Development 课程的其余内容，请升级到 CoddyKit PRO。 Flutter Mobile Development 课程共包含 4 节课。
「单元测试与模拟」这节课中我会学到什么？
为 Flutter 业务逻辑编写快速、隔离的单元测试，并使用模拟对象测试依赖服务和 API 的代码。 你通过在浏览器中直接运行的动手代码来练习 Flutter Mobile Development，全天候 AI 导师会在你学习这节课的过程中回答你的问题。
学习 Flutter Mobile Development 需要有经验吗？
无需任何先前经验。CoddyKit 上的 Flutter Mobile Development 课程适合初学者到高级学习者，你可以从这里开始或从头开始，按照自己的节奏学习。 这是第 4 节课，共 4 节。
「单元测试与模拟」课时需要多长时间？
大多数 CoddyKit 课程大约需要 5–10 分钟。每节课都很精短且互动，所以你能稳步进步，并在网页和应用中从离开的地方继续。
我能在这节 Flutter Mobile Development 课中编写并运行代码吗？
能。每节 Flutter Mobile Development 课都包含内置代码编辑器，你可以在浏览器中直接编写并运行真实代码，并获得即时 AI 反馈 — 无需本地设置。