PowerMock详解

- 概述

PowerMock有两个重要的注解：
@RunWith(PowerMockRunner.class)
@prepareForTest({MyObect.class})
@PrepareForTest注解和@RunWith注解是结合使用的，不要单独使用它们中的任何一个，否则不起作用。当使用
PowerMock去mock静态，final或者私有方法时，需要加上这两个注解。

注意，在你输入@RunWith注解时，Eclipse会自动导入org.powermock.modules.junit4.legacy.PowerMockRunner包，记得把它换成org.powermock.modules.junit4.PowerMockRunner，否则会抛java.lang.NoClassDefFoundError.

- 普通Mock(1)

测试目标代码：

public boolean callArgumentInstance(File file) {
     return file.exists();
}

测试用例代码： 

@Test 
public void testCallArgumentInstance() {
    File file = PowerMockito.mock(File.class); 
    ClassUnderTest underTest = new ClassUnderTest();
    PowerMockito.when(file.exists()).thenReturn(true);
    Assert.assertTrue(underTest.callArgumentInstance(file)); 
}

说明：普通Mock不需要加@RunWith和@PrepareForTest注解。

- 普通Mock(2)

测试目标代码：

public String getFilePath() {
    return path;
}

public String getPayloadName() {
    String pathWithName = getFilePath();
    try {
        int index = pathWithName.lastIndexOf(Constant.SLASH);
	return pathWithName.substring(index + 1);
    }
    catch (Exception e) {
	return pathWithName;
    }
}

测试用例代码： 

@Test
public void testGetPayloadName() throws Exception {
    FileItem item = PowerMockito.mock(FileItem.class);
    String filePath = "../../../test/updates/Citrix.ibr";
    PowerMockito.when(item.getFilePath()).thenReturn(filePath);
    PowerMockito.when(item, "getPayloadName").thenCallRealMethod();
    assertEquals("Citrix.ibr", item.getPayloadName());
}

说明：当使用mock出来的对象去调用某个方法时，要对该方法使用thenCallRealMethod().

- whenNew

测试目标代码：

public class ClassUnderTest {
    public boolean callInternalInstance(String path) { 
        File file = new File(path); 
        return file.exists(); 
    } 
}

测试用例代码：    

@RunWith(PowerMockRunner.class)
@PrepareForTest(ClassUnderTest.class)
public class TestClassUnderTest {
    @Test  
    public void testCallInternalInstance() throws Exception { 
        File file = PowerMockito.mock(File.class); 
        ClassUnderTest underTest = new ClassUnderTest(); 
        PowerMockito.whenNew(File.class).withArguments("bing").thenReturn(file); 
        PowerMockito.when(file.exists()).thenReturn(true); 
        Assert.assertTrue(underTest.callInternalInstance("bing")); 
    }
}

说明：当使用PowerMockito.whenNew方法时，必须加@PrepareForTest和@RunWith注解。注解@PrepareForTest里写的类是需要mock的new对象代码所在的类。

- Mock final方法

测试目标代码：

public class ClassUnderTest{
    public boolean callFinalMethod(Dependency d){
	return d.isAlive();
    }
}
class Dependency{
    public final boolean isAlive(){
	// do something
	return true;
    }
}

测试用例代码：

@RunWith(PowerMockRunner.class) 
public class TestClassUnderTest {
    @Test 
    @PrepareForTest(Dependency.class) 
    public void testCallFinalMethod() {
        Dependency depencency =  PowerMockito.mock(Dependency.class);
        ClassUnderTest underTest = new ClassUnderTest();
        PowerMockito.when(depencency.isAlive()).thenReturn(true);
        Assert.assertTrue(underTest.callFinalMethod(depencency));
    }
}

 说明： 当需要mock final方法的时候，必须加@PrepareForTest和@RunWith注解,@PrepareForTest里写的类是final方法所在的类。
 

- Mock私有方法

测试目标代码：

public class ClassUnderTest{
    public boolean callPrivateMethod(){
	return isAlive();
    }
    private boolean isAlive(){
	// do something
	return true;
    }
}

测试用例代码：

@RunWith(PowerMockRunner.class) 
@PrepareForTest(ClassUnderTest.class) 
public class TestClassUnderTest {
    @Test 
    public void testCallFinalMethod() {
        ClassUnderTest underTest = new ClassUnderTest();
	PowerMockito.when(underTest.callPrivateMethod().thenCallRealMethod();
        PowerMockito.when(underTest, "isAlive").thenReturn(true);
        Assert.assertTrue(underTest.callPrivateMethod());
    }
}

说明： 和mock final方法一样，必须加@PrepareForTest和@RunWith注解,@PrepareForTest里写的类是private方法所在的类。

- Mock静态方法

测试目标代码：

public class ClassUnderTest{
    public boolean callStaticMethod(Dependency d){
	return Dependency.isExist();
    }
}
class Dependency{
    public static boolean isExist(){
	// do something
	return true;
    }
}

测试用例代码：

@RunWith(PowerMockRunner.class) 
public class TestClassUnderTest {
    @Test 
    @PrepareForTest(Dependency.class) 
    public void testCallFinalMethod() {
        PowerMockito.mockStatic(Dependency.class);
        ClassUnderTest underTest = new ClassUnderTest();
        PowerMockito.when(Dependency.isExist()).thenReturn(true);
        Assert.assertTrue(underTest.callStaticMethod(depencency));
    }
}

说明： mock静态方法时需要加@PrepareForTest和@RunWith注解，@PrepareForTest注解中是静态方法所在的类。

- suppress

测试目标代码：

public class RefreshMgmt{
    private static final String MSG_DOWNLOAD_FAILED = Messages.getString("RefreshThread.0");
    public boolean downloadFiles(String path) {
        return download(path);
    }
    private boolean download(String localPath){
	// do something
	return false;
    }
}

测试用例代码：

@RunWith(PowerMockRunner.class)
@PrepareForTest({ RefreshMgmt.class, Messages.class })
public class TestRefreshMgmt {
    @Test
    public void testDownloadFiles() throws Exception {
        PowerMockito.suppress(PowerMockito.method(Messages.class, "getString",  String.class));
	//PowerMockito.suppress(PowerMockito.field(RefreshMgmt.class,  "MSG_DOWNLOAD_FAILED");
        RefreshMgmt mgmt = PowerMockito.mock(RefreshMgmt.class);
        PowerMockito.when(mgmt, "download", Matchers.anyString()).thenReturn(true);
        PowerMockito.when(mgmt.downloadFiles(Matchers.anyString())).thenCallRealMethod();
        assertTrue(mgmt.downloadFiles("C:/temp"));
    }
}

说明： PowerMockito.suppress方法原来禁用某个域或方法，在本例中初始化Messages类会抛出空指针异常，因
此用suppress方法来跳过这个field的初始化。

• PowerMockito.suppress(PowerMockito.constructor(BaseEntity.class))表示禁用BaseEntity的构造函数
• PowerMockito.suppress(PowerMockito.constructor(BaseEntity.class, String.class,  Integer.class))表示禁用参数为String和Integer类型的BaseEntity构造方法。
• PowerMockito.suppress(PowerMockito.method(BaseEntity.class, "performAudit", String.class))表示禁用BaseEntity的performAudit方法。
• @SuppressStaticInitializationFor("BaseEntity")表示禁用BaseEntity的静态初始化。注意引号部分通常需要全名，比如"com.gitshah.powermock.BaseEntity"。
• PowerMockito.suppress(PowerMockito.field(BaseEntity.class,"identifier"))：禁用identifier域。

- WhiteBox

测试目标代码：

public class CataElement{
    private boolean isAvailable = false;
    private List items = new ArrayList<>();
    private Date parseDate(String date) {
    if(!isAvailable)
	return null;
        SimpleDateFormat sdf = new SimpleDateFormat("MM/dd/yyyy");
        try {
            if (date == null || date.isEmpty())
                return null;
            return sdf.parse(date);
        }
        catch (ParseException e) {
            Log.log(Log.WARN, e, getClass());
            return null;
        }
    }
}

测试用例代码：

public class CataElementTest{
    @Test
    public void test(){
        CataElement e = new CataElement();
        Whitebox.setInternalState(e, "isAvailable", true);
        // other things
	List items = Whitebox.getInternalState(e, "items");
	assertTrue(items.size == 0);
    }
}

• Whitebox.setInternalState(object, "fieldName", value)可以设置某个对象的某个field。
• Whitebox.getInternalState(object, "fieldName")获取某个对象的某个field的值。
• Whitebox.invokeMethod(object, methodName, para)可以调用私有方法，测试私有方法的返回值。
  

- Answer

测试用例代码：

@Test
public void test() {
    final EmployeeService mock = PowerMockito.mock(EmployeeService.class);
    final Employee employee = new Employee();
    PowerMockito.when(mock.findEmployeeByEmail(Matchers.anyString())).then(new Answer() {
	public Employee answer(InvocationOnMock invocation) throws Throwable {
	    final String email = (String) invocation.getArguments()[0];
	    if(email == null) return null;
	    if(email.startsWith("deep")) return employee;
	    if(email.endsWith("packtpub.com")) return employee;
	    return null;
	}
    });
    final EmployeeController employeeController = new EmployeeController(mock);
    assertSame(employee, employeeController.findEmployeeByEmail("[email protected]"));
    assertSame(employee, employeeController.findEmployeeByEmail("[email protected]"));
    assertNull(employeeController.findEmployeeByEmail("[email protected]"));
}

说明：改测试方法根据不同的参数返回不同的结果，Answer的泛型类型必须和answer方法的返回值类型一致。
Answer接口指定执行的action和返回值。Answer的参数是InvocationOnMock的实例，支持：
callRealMethod()：调用真正的方法
getArguments()：获取所有参数
getMethod()：返回mock实例调用的方法
getMock()：获取mock实例