PowerMock用法

最近一直在用PowerMock做Unit test的Object mock(对象模拟)。总结了一些经验和发现了一些须要注意事项，俗语说的好“好记性不如烂笔头”，为方便日后参考，于是把它们写下来。

         说到PowerMock不得不提EasyMock, 如果日常工作中要实现一些对象的Mock（如，写一些Unit test）,大家对EasyMock应该会有所了解, 正是由于EasyMock在复杂情况下的表现不佳，则有了后面的PowerMock。这里简单罗列一下EasyMock一些不足之处：

1） 3.0以前只能Mock interface不能Mock Class。（3.0以前要引放Mock class extension实现Mock class）。

2）不能够Mock 静态方法，final方法，private方法和构造函数。



然后这些不足之处对PowerMock来说是很容易实现的，因为PowerMock实现机制与EasyMock不一样，EasyMock是用的proxy的方式实现在的Mock，而PowerMock则是使用Cglib直接修改的字节码。



现在来说一下一些具体一点用法：

(一)   Mock class public method



public class ExampleClass {

    public String getMsg(String s){

       if ("yes".equals(s)){

           return "yes";

       } else {

           return "no";

       }

    }

  

    public String getTest(String s){

       return this.getMsg(s);

    }

}

       如上所示类，请见unit teset

@RunWith(PowerMockRunner.class)

@PrepareForTest({ExampleClass.class})

public class ExampleClassTest {



    @Test

    public void testGetMsg() {    

       ExampleClass ec = PowerMock.createPartialMock(ExampleClass.class, "getMsg");

       EasyMock.expect(ec.getMsg("test")).andReturn("PowerMock");

       PowerMock.replay(ec);

     

       assertEquals("PowerMock", ec.getTest("test"));

    }



}



本例用PowerMock mock了ExampleClass的部分method getMsg(…),由上看出本类实则有两个方法，另一个是getTest(…)。如果采用如下代码

ExampleClass ec = PowerMock.createMock(ExampleClass.class);

       EasyMock.expect(ec.getMsg("test")).andReturn("PowerMock");

后面的ec.getTest(“test”)将会抛异常

                            java.lang.AssertionError:

                                   Unexpected method call getTest("test"):

因为此时mock对象ec仅被指定有一个方法getMsg。



(二)   Mock class static method



public class IdGenerator {

   public static long generateNewId() {

      return System.currentTimeMillis();

   }

}

public class StaticClassSample {

    public long registerService(Object service) {

       final long id = IdGenerator.generateNewId();

       return id;

    }

}



@RunWith(PowerMockRunner.class)

@PrepareForTest( {StaticClassSample.class, IdGenerator.class})

public class StaticClassSampleTest { 

    @Test

    public void testRegisterService() throws Exception {

            long expectedId = 42;

            PowerMock.mockStatic(IdGenerator.class);

EasyMock.expect(IdGenerator.generateNewId()).andReturn(expectedId);

            PowerMock.replay(IdGenerator.class);

            long actualId = new StaticClassSample().registerService(new Object());

            Assert.assertEquals(expectedId, actualId);

            PowerMock.verify(IdGenerator.class);

    }

}

(三)   Mock class private method



public class DataService {



    public boolean replaceData(final String dataId, final byte[] binaryData) {

            return modifyData(dataId, binaryData);

    }

    public boolean deleteData(final String dataId) {

            return modifyData(dataId, null);

    }

  

    private boolean modifyData(final String dataId, final byte[] binaryData) {

            return true;

    }

}



@RunWith(PowerMockRunner.class)

@PrepareForTest( {DataService.class})

public class DataServiceTest {

    @Test

    public void testReplaceData() throws Exception {

            final String modifyDataMethodName = "modifyData";

            final byte[] expectedBinaryData = new byte[] { 42 };

            final String expectedDataId = "id";

            DataService tested = createPartialMock(DataService.class, modifyDataMethodName);

            expectPrivate(tested, modifyDataMethodName, expectedDataId,

                            expectedBinaryData).andReturn(true);

            replay(tested);

            Assert.assertTrue(tested.replaceData(expectedDataId, expectedBinaryData));

            verify(tested);

    }

}



(四)   Mock class constructor



public class PersistenceManager {



    public boolean createDirectoryStructure(String directoryPath) {

            File directory = new File(directoryPath);



            if (directory.exists()) {

                    throw new IllegalArgumentException("/"" + directoryPath + "/" already exists.");

            }



            return directory.mkdirs();

    }

}



@RunWith(PowerMockRunner.class)

@PrepareForTest( PersistenceManager.class )

public class PersistenceManagerTest {



        @Test

        public void testCreateDirectoryStructure_ok() throws Exception {

                final String path = "directoryPath";

                File fileMock = PowerMock.createMock(File.class);



                PersistenceManager tested = new PersistenceManager();



                PowerMock.expectNew(File.class, path).andReturn(fileMock);



                EasyMock.expect(fileMock.exists()).andReturn(false);

                EasyMock.expect(fileMock.mkdirs()).andReturn(true);



                PowerMock.replay(fileMock, File.class);



                Assert.assertTrue(tested.createDirectoryStructure(path));



                PowerMock.verify(fileMock, File.class);

        }

}





上面就是PowerMock的一些比较基本的用法