您如何模拟设置只读属性的void方法？

Question

I'm not very familiar with RhinoMocks and I'm trying to break into TDD on a side project of mine. I've been moving along okay until I hit a wall trying to get this behavior under test.

    private int _result;
    public int Result { get { return _result; } }

    public void GetRandomValue()
    {
        Random n = new Random();
        _result = n.Next(1,100);
    }

Since this is an abstract class, how can I use RhinoMocks to verify that when I call the GetRandomValue method that the Result property is set? Or is this a necessary test? Or a better way to design this small bit of code?

Answer 1

The way I would go about testing it is

var randomizerClass = new RandomizerClass();
ranomizerClass.GetRandomValue();
var result = ranomizerClass.Result;

Assert.IsTrue(result > 0 && result < 101);

And the ranomizerClass is the concrete implementation of the abstract class. You don't need to separately test your abstract class since that will be done through the concrete implementation

Answer 2

也许您应该从抽象类中提取接口，并简单地使用相应的方法为其实现模拟？

Answer 3

Presumably when you instantiate the type, the _result field is set to it's default value of 0. So can't you just create an instance of the type, call the method, and then check the value of the Result property doesn't equal 0?

It seems odd that a method called GetRandomValue , doesn't actually return anything. Is there a reason why this method doesn't return the result? Also, I would instantiate your Random type outside the scope of the method.

Answer 4

How can you test that you're getting a random number? It's random, so you can't write a test that's actually asserting anything useful. You could make an IRandomNumberProvider interface and implement it on a RandomNumberProvider , then mock that for testing purposes, but you wouldn't be testing anything of value in my opinion. Even if you did like some other folks suggested and asserted that the number is between 1 and 100, you haven't tested anything useful in your code, you've just ensured that Microsoft's implementation of Next is working, which is a given.

Your GetRandomValue() method shouldn't set Result , though. It should return the result. Otherwise, you've introduced a side effect into your class, and that generally can cause weird, hard-to-track-down bugs.

Answer 5

In the cases where you need to test functionality in an abstract class, simply create a class that implements it in your test project.

Eg given the following class

public abstract class MyClass
{
    private int _result;     
    public int Result { get { return _result; } }      
    public void GetRandomValue()     
    {         
        Random n = new Random();         
        _result = n.Next(1,100);     
    }
}

Create a test class in your test project

public class StubMyClass : MyClass
{ 
} 

and then test it as follows

[Test]
public void ShouldSetResultAfterCallingGetRandomValue()
{ 
    var myClass = new StubMyClass();
    myClass.GetRandomValue();
    int expected = 1234;
    Assert.That(myClass.Result, Is.EqualTo(expected));
}