Powermock：如何在静态类中模拟私有方法

Question

Let's say that I have a utility class like this:

public final class NumberUtility{

public static int getNumberPlusOne(int num){

   return doSomethingFancyInternally(num);

}

private static int doSomethingFancyInternally(int num){

      //Fancy code here...

  return num;

}

}

Assuming that I don't change the class's structure, how do mock the doSomethingFancyInternally() method with the use of Powermock?

Answer 1

Why you cannot mock getNumberPlusOne method with PowerMock ? Private method shouldn't be visible in tests.

For example someone change internal implementation of private method ( change method name even) then your test will fail.

Answer 2

you can use java reflection to access private method in a class . So similar way you can test this private method.

Answer 3

Usually to test such a situations the Bypass encapsulation technique can be used. Here is the example of this: https://code.google.com/p/powermock/wiki/BypassEncapsulation . Frankly speaking it just hacks the class privacy with use of the java reflection API, so you're not forced to change your class strcuture to test it.

Answer 4

This should help-> Mocking a private static method on a class

http://avricot.com/blog/index.php?post/2011/01/25/powermock-%3A-mocking-a-private-static-method-on-a-class

Here's my code for your class. I modified your CUT too.

TEST CLASS:

import org.easymock.EasyMock;
import org.junit.Assert;
import org.junit.Before;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.powermock.api.easymock.PowerMock;
import org.powermock.core.classloader.annotations.PrepareForTest;
import org.powermock.modules.junit4.PowerMockRunner;

@RunWith(PowerMockRunner.class)    
@PrepareForTest({ NumberUtility.class })
public class NumberUtilityTest {

// Class Under Test
NumberUtility cut;

@Before
public void setUp() {

    // Create a new instance of the service under test (SUT).
    cut = new NumberUtility();

    // Common Setup
    // TODO
}

/**
 * Partial mocking of a private method.
 * 
 * @throws Exception
 * 
 */
@Test
public void testGetNumberPlusOne1() throws Exception {

    /* Initialization */
    PowerMock.mockStaticPartial(NumberUtility.class,
            "doSomethingFancyInternally");
    NumberUtility partialMockCUT = PowerMock.createPartialMock(
            NumberUtility.class, "doSomethingFancyInternally");
    Integer doSomethingFancyInternallyOutput = 1;
    Integer input = 0;

    /* Mock Setup */
    PowerMock
            .expectPrivate(partialMockCUT, "doSomethingFancyInternally",
                    EasyMock.isA(Integer.class))
            .andReturn(doSomethingFancyInternallyOutput).anyTimes();

    /* Activate the Mocks */
    PowerMock.replayAll();

    /* Test Method */
    Integer result = NumberUtility.getNumberPlusOne(input);

    /* Asserts */
    Assert.assertEquals(doSomethingFancyInternallyOutput, result);
    PowerMock.verifyAll();

}

}

CUT: public final class NumberUtility{

public static Integer getNumberPlusOne(Integer num){

return doSomethingFancyInternally(num);} 

private static Integer doSomethingFancyInternally(Integer num){

  //Fancy code here...

return num;} 

}