mockito中兩種部分mock的實現，spy、callRealMethod

 

什么是類的部分mock（partial mock）？
A：部分mock是說一個類的方法有些是實際調用，有些是使用mockito的stubbing（樁實現）。

 

為什么需要部分mock？

A：當需要測試一個組合方法（一個方法需要其它多個方法協作）的時候，某個葉子方法（只供別人調用，自己不依賴其它反復）已經被測試過，我們其實不需要再次測試這個葉子方法，so，讓葉子打樁實現返回結果，上層方法實際調用並測試。

mockito實現部分mock的兩種方式：spy和callRealMethod()

spy實現：

package spy;

import static org.junit.Assert.*;
import static org.mockito.Mockito.*;
import java.util.LinkedList;
import java.util.List;

import org.junit.Test;

public class SpyDemo {

    @Test
    public void spy_Simple_demo(){
        List<String> list = new LinkedList<String>();  
        List<String> spy = spy(list);  
        when(spy.size()).thenReturn(100);  
        
        spy.add("one");  
        spy.add("two");  
        
/*        spy的原理是，如果不打樁默認都會執行真實的方法，如果打樁則返回樁實現。
        可以看出spy.size()通過樁實現返回了值100，而spy.get(0)則返回了實際值*/
        assertEquals(spy.get(0), "one");  
        assertEquals(100, spy.size());  
    }
    
    @Test  
    public void spy_Procession_Demo() {  
        Jack spyJack = spy(new Jack());  
        //使用spy的樁實現實際還是會調用stub的方法，只是返回了stub的值
        when(spyJack.go()).thenReturn(false);  
        assertFalse(spyJack.go()); 
        
        //不會調用stub的方法
        doReturn(false).when(spyJack).go();
        assertFalse(spyJack.go()); 
    } 
    
}



class Jack {  
    public boolean go() {  
        System.out.println("I say go go go!!");  
        return true;  
    }  
}

 

Spy類就可以滿足我們的要求。如果一個方法定制了返回值或者異常，那么就會按照定制的方式被調用執行；如果一個方法沒被定制，那么調用的就是真實類的方法。

如果我們定制了一個方法A后，再下一個測試方法中又想調用真實方法，那么只需在方法A被調用前，調用Mockito.reset(spyObject);就行了。

package spy;

import static org.mockito.Mockito.when;

import org.mockito.Mockito;

public class TestMockObject {

    public static void main(String[] args) {

        TestMockObject mock = Mockito.mock(TestMockObject.class);
        System.out.println(mock.test1());
        System.out.println(mock.test2());

        TestMockObject spy = Mockito.spy(new TestMockObject());
        System.out.println(spy.test1());
        System.out.println(spy.test2());

        when(spy.test1()).thenReturn(100);
        System.out.println(spy.test1());

        Mockito.reset(spy);
        System.out.println(spy.test1());
        System.out.println(spy.test2());

        when(spy.test1()).thenReturn(104);
        System.out.println(spy.test1());
    }

    public int test1() {
        System.out.print("RealTest1()!!! - ");
        return 1;
    }

    public int test2() {
        System.out.print("RealTest2()!!! - ");
        return 2;
    }

}

 

輸出為：

0
0
RealTest1()!!! - 1
RealTest2()!!! - 2
RealTest1()!!! - 100
RealTest1()!!! - 1
RealTest2()!!! - 2
RealTest1()!!! - 104

要注意的是，對Spy對象的方法定制有時需要用另一種方法：
===============================================================================
Importantgotcha on spying real objects!

Sometimes it's impossible to usewhen(Object) for stubbing spies. Example:
List list = new LinkedList();
List spy = spy(list);

//Impossible: real method is called so spy.get(0) throwsIndexOutOfBoundsException (the list is yet empty)
when(spy.get(0)).thenReturn("foo");

//You have to use doReturn() for stubbing
doReturn("foo").when(spy).get(0);
===============================================================================
因為用when(spy.f1())會導致f1()方法被真正執行，所以就需要另一種寫法。

http://blog.csdn.net/dc_726/article/details/8568537

 

 

callRealMethod()實現

Use doCallRealMethod() when you want to call the real implementation of a method.

As usual you are going to read the partial mock warning: Object oriented programming is more less tackling complexity by dividing the complexity into separate, specific, SRPy objects. How does partial mock fit into this paradigm? Well, it just doesn't... Partial mock usually means that the complexity has been moved to a different method on the same object. In most cases, this is not the way you want to design your application.

However, there are rare cases when partial mocks come handy: dealing with code you cannot change easily (3rd party interfaces, interim refactoring of legacy code etc.) However, I wouldn't use partial mocks for new, test-driven & well-designed code.

See also javadoc Mockito.spy(Object) to find out more about partial mocks. Mockito.spy() is a recommended way of creating partial mocks. The reason is it guarantees real methods are called against correctly constructed object because you're responsible for constructing the object passed to spy() method.

Example:

   Foo mock = mock(Foo.class);
   doCallRealMethod().when(mock).someVoidMethod();

   // this will call the real implementation of Foo.someVoidMethod()
   mock.someVoidMethod();
 

See examples in javadoc for Mockito class

Returns:

stubber - to select a method for stubbing

 

package callRealMethod;

import org.junit.Test;
import static org.mockito.Mockito.*;

public class CallMethodDemo {
    @Test  
    public void callRealMethodTest() {  
        Jerry jerry = mock(Jerry.class);  
      
        doCallRealMethod().when(jerry).goHome();  
        doCallRealMethod().when(jerry).doSomeThingB();  
      
        jerry.goHome();  
      
        verify(jerry).doSomeThingA();  
        verify(jerry).doSomeThingB();  
    }  
}

class Jerry {  
    public void goHome() {  
        doSomeThingA();  
        doSomeThingB();  
    }  
  
    // real invoke it.  
    public void doSomeThingB() {  
        System.out.println("good day");  
  
    }  
  
    // auto mock method by mockito  
    public void doSomeThingA() {  
        System.out.println("you should not see this message.");  
  
    }  
}

  通過代碼可以看出Jerry是一個mock對象， goHome()和doSomeThingB()是使用了實際調用技術，而doSomeThingA()被mockito執行了默認的answer行為（這里是個void方法，so，什么也不干）。

 

總結：

    spy和callrealmethod都可以實現部分mock，唯一不同的是通過spy做的樁實現仍然會調用實際方法（我都懷疑這是不是作者的bug）。

   ★ 批注：spy方法需要使用doReturn方法才不會調用實際方法。

 

    mock技術是實施TDD過程必備的裝備，熟練掌握mockito（或者其他工具）可以更有效的進行測試。雖然mockito作者也覺得部分測試不是好的設計，但是在java這樣一個不是完全面向對象技術的平台上，我們其實沒必要過分糾結這些細節，簡潔，可靠的代碼才是我們需要的。

http://heipark.iteye.com/blog/1496603