如何使用数据库查询对对象进行单元测试 [英] How to unit test an object with database queries

问题描述

我听说单元测试非常棒"、非常酷"和各种各样的好东西"，但我 70% 或更多的文件涉及数据库访问(一些读取和一些写入)，我不确定如何为这些文件编写单元测试.

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.

我正在使用 PHP 和 Python，但我认为这是一个适用于大多数/所有使用数据库访问的语言的问题.

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

推荐答案

我建议模拟您对数据库的调用.模拟基本上是看起来像您试图调用方法的对象的对象，从某种意义上说，它们具有相同的属性、方法等，可供调用者使用.但是，当调用特定方法时，它不会执行它们被编程为执行的任何操作，而是完全跳过该操作，只返回一个结果.该结果通常由您提前定义.

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.

为了设置用于模拟的对象，您可能需要使用某种控制反转/依赖注入模式，如下面的伪代码所示:

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();
    }
}

现在在您的单元测试中，您创建了 FooDataProvider 的模拟，它允许您调用 GetAllFoos 方法而无需实际访问数据库.

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)
    }
}

简而言之，一个常见的模拟场景.当然，您可能仍然希望对实际的数据库调用进行单元测试，为此您需要访问数据库.

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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