如何用数据库查询单元测试对象 [英] How to unit test an object with database queries

问题描述

我听说单元测试是完全真棒，真的很酷和各种各样的好东西，但70％或更多的我的文件涉及数据库访问（一些读和一些写）不知道如何写这些文件的单元测试。

我使用PHP和Python，但我认为这是一个问题，适用于大多数/所有语言使用数据库访问。

解决方案

我建议嘲笑你的数据库调用。 Mocks基本上是对象，看起来像你试图调用一个方法的对象，在它们具有相同的属性，方法等可用于调用者的意义上。但是，当调用特定方法时，它不是执行它们被编程的任何动作，而是完全跳过，并且返回结果。这个结果通常由你提前定义。

为了设置你的对象进行嘲笑，你可能需要使用某种反转的控制/依赖注入模式，如下面的伪代码： / p>

  class Bar 
 {
 private FooDataProvider _dataProvider; 
 
 public instantiate（FooDataProvider dataProvider）{
 _dataProvider = dataProvider; 
} 
 
 public getAllFoos（）{
 //而不是调用Foo.GetAll（）在这里，我们引入一个额外的抽象层
 return _dataProvider.GetAllFoos （）; 
} 
} 
 
 class FooDataProvider 
 {
 public Foo [] GetAllFoos（）{
 return Foo.GetAll 
} 
} 
  

现在在你的单元测试中，你创建一个模拟FooDataProvider，它允许你调用方法GetAllFoos而不必实际命中数据库。

  class BarTests 
 {
 public TestGetAllFoos（）{
 //这里我们设置我们的mock FooDataProvider 
 mockRepository = MockingFramework.new（）
 mockFooDataProvider = mockRepository.CreateMockOfType（FooDataProvider）; 
 
 //创建一个新的Foo对象数组
 testFooArray = new Foo [] {Foo.new（），Foo.new（），Foo.new（）} 
 
 //下一条语句将导致每当我们调用FooDAtaProvider.GetAllFoos，
 //时返回testFooArray，而不是调用数据库并返回任何内容
 // ExpectCallTo和Returns是我们假想的模拟框架提供的方法
 ExpectCallTo（mockFooDataProvider.GetAllFoos）.Returns（testFooArray）
 
 //现在开始我们的实际单元测试
 testBar = new Bar（mockFooDataProvider） 
 baz = testBar.GetAllFoos（）
 
 // baz现在应该等于我们之前创建的testFooArray对象
 Assert.AreEqual（3，baz.length）
} 
} 
  

一个常见的嘲笑场景。当然，你仍然可能想要单元测试你的实际数据库调用，你需要打到数据库。

I've heard that unit testing is "totally awesome", "really cool" and "all manner of good things" but 70% or more of my files involve database access (some read and some write) and I'm not sure how to write a unit test for these files.

I'm using PHP and Python but I think it's a question that applies to most/all languages that use database access.

解决方案

I would suggest mocking out your calls to the database. Mocks are basically objects that look like the object you are trying to call a method on, in the sense that they have the same properties, methods, etc. available to caller. But instead of performing whatever action they are programmed to do when a particular method is called, it skips that altogether, and just returns a result. That result is typically defined by you ahead of time.

In order to set up your objects for mocking, you probably need to use some sort of inversion of control/ dependency injection pattern, as in the following pseudo-code:

class Bar
{
    private FooDataProvider _dataProvider;

    public instantiate(FooDataProvider dataProvider) {
        _dataProvider = dataProvider;
    }

    public getAllFoos() {
        // instead of calling Foo.GetAll() here, we are introducing an extra layer of abstraction
        return _dataProvider.GetAllFoos();
    }
}

class FooDataProvider
{
    public Foo[] GetAllFoos() {
        return Foo.GetAll();
    }
}

Now in your unit test, you create a mock of FooDataProvider, which allows you to call the method GetAllFoos without having to actually hit the database.

class BarTests
{
    public TestGetAllFoos() {
        // here we set up our mock FooDataProvider
        mockRepository = MockingFramework.new()
        mockFooDataProvider = mockRepository.CreateMockOfType(FooDataProvider);

        // create a new array of Foo objects
        testFooArray = new Foo[] {Foo.new(), Foo.new(), Foo.new()}

        // the next statement will cause testFooArray to be returned every time we call FooDAtaProvider.GetAllFoos,
        // instead of calling to the database and returning whatever is in there
        // ExpectCallTo and Returns are methods provided by our imaginary mocking framework
        ExpectCallTo(mockFooDataProvider.GetAllFoos).Returns(testFooArray)

        // now begins our actual unit test
        testBar = new Bar(mockFooDataProvider)
        baz = testBar.GetAllFoos()

        // baz should now equal the testFooArray object we created earlier
        Assert.AreEqual(3, baz.length)
    }
}

A common mocking scenario, in a nutshell. Of course you will still probably want to unit test your actual database calls too, for which you will need to hit the database.

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