如何对创建实例的单元进行测试？ [英] How to unit test instance creation?

问题描述

我有一个 Carpenter 类，它使用 Lathe 和 Wood进行工作对象。

I have a Carpenter class that does it's work using a Lathe and a Wood object.

class Carpenter
{
    function Work()
    {
        $tool = new Lathe();
        $material = new Wood();
        $tool->Apply($material);
    }
}

车床依赖于称为 Material 的接口，因此我可以通过为其提供伪造的<$来轻松地对 Lathe 进行单元测试。 c $ c>材料在我的单元测试中。 Wood 不依赖任何东西，因此也可以轻松测试。

Lathe depends on an interface called Material, so I can easily unit test Lathe by giving it a fake Material in my unit test. Wood doesn't depend on anything, so it can also be easily tested.

interface Material {
    // Various methods...
}

interface Tool {
    function Apply(Material $m);
}

class Wood implements Material  {
    // Implementations of Material methods
}

class Lathe {
    function Apply(Material $m) {
        // Do processing
    }
}

但是，木匠取决于具体类车床和木，因为它必须创建它们的实例。这意味着，按照目前的情况，如果不经意引入 Lathe 和<$就不能对 Work（）方法进行单元测试c $ c> Wood 进行测试。

However, Carpenter depends on the concrete classes Lathe and Wood because it has to create instances of them. That means that as it currently stands, I cannot unit test the Work() method without inadvertantly bringing Lathe and Wood under test.

我应该如何将设计更改为单元测试 Carpenter ？

How should I change my design to unit test Carpenter?

推荐答案

您可以在以下两个不同的方向进行操作：

There's a couple of different directions you can take here:

• 使用构造函数注入，只需将工具和材质实例注入木匠即可。


• 如果由于某些原因无法注入实例（也许是因为您需要为每次调用Work方法创建新实例），则可以注入 Abstract Factories 。


• 您还可以使用ctford描述的 Factory方法方法，但这需要您还创建特定于测试的替代值以进行单元测试，但这是完全有效的做法要做的只是更多的工作，在许多情况下，其他选择会更好，更灵活。

• Use Constructor Injection and simply inject the tool and the material instances into the carpenter.
• If injecting instances doesn't work for some reason (perhaps because you need to create new instances for every invocation of the Work method), you can inject Abstract Factories instead.
• You can also use the Factory Method approach described by ctford, but that requires you to also create test-specific overrides to be able to unit test, and while that's a completely valid thing to do, it's just more work and in many cases the other alternatives are better and more flexible.

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