如何单元测试将文件保存到磁盘? [英] How do I unit-test saving file to the disk?

问题描述

我知道强烈建议运行单元测试与文件系统分离，因为如果你在测试中接触文件系统，你也测试文件系统本身.好的，这很合理.
我的问题是，如果我想测试文件保存到磁盘，我该怎么做?与数据库一样，我将负责数据库访问的接口分开，然后为我的测试创建另一个实现?或者可能有其他方式?

I know that it's strongly recommended to run unit-tests in separation from file system, because if you do touch file system in your test, you also test file system itself. OK, that's reasonable.
My question is, if I want to test file saving to the disk, what do I do? As with database, I separate an interface that is responsible for database access, and then create another implementation of this for my tests? Or may be there's some other way?

推荐答案

我对此的方法严重偏向于 由测试指导的成长型面向对象软件(GOOS)书，我刚读过，但它是我今天所知道的最好的.具体:

My approach towards this is heavily biased on the Growing Object-Oriented Software Guided by Tests (GOOS) book that I just read, but it's the best that I know of today. Specifically:

• 创建一个接口，从您的代码中抽象出文件系统.在需要这个类作为协作者/依赖项的地方模拟它.这使您的单元测试和反馈快速.
• 创建集成测试来测试接口的实际实现.即验证调用 Save() 实际上将文件持久化到磁盘并具有写入内容(使用参考文件或解析它以获取它应该包含的一些内容)
• 创建一个验收测试来测试整个系统 - 端到端.您可以在此处验证是否创建了文件 - 此测试的目的是确认实际实现是否正确连接/插入.

评论者更新:

如果您正在阅读结构化数据(例如 Book 对象)(如果不是用字符串替换 IEnumerable)

If you're reading structured data (e.g. Book objects) (If not substitute string for IEnumerable)

interface BookRepository
{
  IEnumerable<Books> LoadFrom(string filePath);
  void SaveTo(string filePath, IEnumerable<Books> books);
}

现在您可以使用构造函数注入将模拟注入客户端类.客户端类单元测试因此很快；不要点击文件系统.他们只是验证在依赖项上调用了正确的方法(例如加载/保存)

Now you can use constructor-injection to inject a mock into the client class. The client class unit tests therefore are fast ; do not hit the filesystem. They just verify that the right methods are called on the dependencies (e.g. Load/Save)

var testSubject = new Client(new Mock<BookRepository>.Object);

接下来，您需要创建 BookRepository 的真正实现，该实现可以处理文件(如果需要，也可以在明天创建 Sql DB).没有其他人需要知道.为 FileBasedBookRepository(实现上述角色)编写集成测试，并测试使用参考文件调用 Load 会提供正确的对象，并使用已知列表调用 Save，将它们持久化到磁盘.即使用真实文件这些测试会很慢，所以用标签标记它们或将其移到单独的套件中.

Next you need to create the real implementation of BookRepository that works off a File (or a Sql DB tommorrow if you want it). No one else has to know. Write integration tests for FileBasedBookRepository (that implements the above Role) and test that calling Load with a reference file gives the right objects and calling Save with a known list, persists them to the disk. i.e. uses real files These tests would be slow so mark them up with a tag or move it to a separate suite.

[TestFixture]
[Category("Integration - Slow")]
public class FileBasedBookRepository 
{
  [Test]
  public void CanLoadBooksFromFileOnDisk() {...}
  [Test]
  public void CanWriteBooksToFileOnDisk() {...}
}

最后应该有一个/多个验收测试来练习加载和保存.

Finally there should be one/more acceptance tests that exercises Load and Save.

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