用PowerMock mock 临时变量

在开发时，经常遇到这种情况，被测试方法所调用的类不是通过构造注入的，而是通过临时new出来的，如下面待测方法：

public class EmployeeService {
    private EmployeeDao employeeDao;


    public int getTotalEmployeeWithTempVariable() {
        EmployeeDao employeeDao = new EmployeeDao();
        return employeeDao.getTotal();
    }
}

employeeDao是临时new出来的，而mockito和easyＭock一般是通过代理来实现mock,这时就无法mock此类方法了。

而PowerMock通过直接修改class,使这类方法可测，

@PrepareForTest(EmployeeService.class)
public class EmployeeServiceTest extends PowerMockTestCase {

    EmployeeService employeeService;

    @ObjectFactory
    public ITestObjectFactory getObjectFactory() {
        return new PowerMockObjectFactory();
    }
    @BeforeMethod
    public void init(){
         employeeService = new EmployeeService(employeeDao);
    }
    
    @Test
    public void testGetTotalEmployeeWithTempVariable() {
        try {
            PowerMockito.whenNew(EmployeeDao.class).withNoArguments()
                    .thenReturn(employeeDao);
            PowerMockito.when(employeeDao.getTotal()).thenReturn(10);
            int total = employeeService.getTotalEmployeeWithTempVariable();
            assertEquals(10, total);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

这里有三个很重要的地方：

@PrepareForTest(EmployeeService.class)：告诉PowerMock，需要修改EmployeeService的class文件

@ObjectFactory：告诉testNG以对象工厂的形式创建测试实例

extends PowerMockTestCase　：继承此接口

此外需要

PowerMockito.whenNew(EmployeeDao.class).withNoArguments()
.thenReturn(employeeDao);

录制EmployeeDao的构造行为并返回实例