使用JMockit模拟测试类的私有方法 [英] Mocking private method of class under test using JMockit

问题描述

我想模拟一个被测试类的私有方法但是方法在调用方法之后首先返回false两次，之后它应该返回false。
这是我试过的代码。
这是正在测试的类

I want to mock private method of a class under test but method return false first two times when the method is called after that it should return false. Here is the code what I tried. This is the class which is being tested

public class ClassToTest 
{
    public void methodToTest()
    {
        Integer integerInstance = new Integer(0);
        boolean returnValue= methodToMock(integerInstance);
        if(returnValue)
        {
            System.out.println("methodToMock returned true");
        }
        else
        {
            System.out.println("methodToMock returned true");
        }
        System.out.println();
    }
    private boolean methodToMock(int value)
    {
        return true;
    }
}

测试类

import org.junit.Test;
import static mockit.Deencapsulation.*;

import mockit.*;
public class TestAClass 
{
    @Tested ClassToTest classToTestInstance;
    @Test
    public void test1()
    {

        new NonStrictExpectations(classToTestInstance)
        {
            {
                invoke(classToTestInstance, "methodToMock", anyInt);
                returns(false);
                times = 2;

                invoke(classToTestInstance, "methodToMock", anyInt);
                returns(true);
                times = 1;

            }
        };

        classToTestInstance.methodToTest();
        classToTestInstance.methodToTest();
        classToTestInstance.methodToTest();

    }
}

我这样做是为了获得理想的结果

I did this to get desired results

    final StringBuffer count = new StringBuffer("0");
    new NonStrictExpectations(classToTestInstance)
    {

        {
            invoke(classToTestInstance, "methodToMock", anyInt);
            result= new Delegate() 
            {
                boolean methodToMock(int value)
                {                   
                    count.replace(0, count.length(), Integer.valueOf(Integer.valueOf(count.toString())+1).toString());
                    if(Integer.valueOf(count.toString())==3)
                    {
                        return true;
                    }
                    return false;
                }
            };

        }
    };

推荐答案

使用期望（或StrictExpectations）

使用Expectations和Deencapsulation.invoke（）的组合，您可以部分模拟测试对象：

Using Expectations (or StrictExpectations)

Using a combination of Expectations and Deencapsulation.invoke(), you can partially mock the tested object:

import org.junit.Test;
import static mockit.Deencapsulation.*;
import mockit.*;

public class TestAClass
{
    public static class ClassToTest 
    {
        public void methodToTest()
        {
            boolean returnValue = methodToMock(0);
            System.out.println("methodToMock returned " + returnValue);
        }

        private boolean methodToMock(int value) { return true; }
    }

    @Tested ClassToTest classToTestInstance;

    @Test
    public void partiallyMockTestedClass() {
        new Expectations(classToTestInstance) {{
            invoke(classToTestInstance, "methodToMock", anyInt);
            result = false;
            times = 2;
        }};

        classToTestInstance.methodToTest();
        classToTestInstance.methodToTest();
        classToTestInstance.methodToTest();
    }
}

上面的测试打印：

methodToMock returned false
methodToMock returned false
methodToMock returned true

一般来说，我们应该避免模仿私有方法。也就是说，我在实践中发现它 有时候是有用的，通常当你有一个非常重要的私有方法并且已经通过另一个测试进行测试时;在这种情况下，在第二次测试中模拟私有方法（对于不同的公共方法或通过相同公共方法的不同路径）可能比设置必要的输入/条件容易得多。

In general, of course, we should avoid mocking private methods. That said, I have found in practice that it is sometimes useful to do so, typically when you have a private method which does something non-trivial and was already tested by another test; in such a case, mocking that private method in a second test (either for a different public method or a different path through the same public method) may be significantly easier than setting up necessary inputs/conditions.

使用NonStrictExpectations编写测试也很容易（OP的原始尝试没有'只是因为记录了相同的非严格期望两次，第二次记录覆盖了第一次记录：

It's just as easy to write the test with a NonStrictExpectations (the original attempt by the OP didn't work only because the same non-strict expectation was recorded twice, with the second recording overriding the first):

@Test
public void partiallyMockTestedClass() {
    new NonStrictExpectations(classToTestInstance) {{
        invoke(classToTestInstance, "methodToMock", anyInt);
        returns(false, false, true);
    }};

    classToTestInstance.methodToTest();
    classToTestInstance.methodToTest();
    classToTestInstance.methodToTest();
}

使用代表

如果需要更大的灵活性，我们总是可以记录代表的结果：

@Test
public void partiallyMockTestedClass() {
    new NonStrictExpectations(classToTestInstance) {{
        invoke(classToTestInstance, "methodToMock", anyInt);

        result = new Delegate() {
           boolean delegate() {
               boolean nextValue = ...choose next return value somehow...
               return nextValue;
           }
        }
    }};

    classToTestInstance.methodToTest();
    classToTestInstance.methodToTest();
    classToTestInstance.methodToTest();
}

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