PowerMock实践

一、常用注解

@PrepareForTest和@RunWith是成对出现的，一般@RunWith(PowerMockRunner.class)，@PrepareForTest的值是引用的静态方法或私有方法的类。

@InjectMocks注解标注的类会被注入所有被@Mock注解标注的类。

@Before注解用于方法，表示在执行@Test注解标注的方法之前执行。

在initMocks()方法中可以执行MockitoAnnotations.initMocks(this);来将@Mock注解修饰的类注入到@InjectMocks修饰的类。

二、实例操作

首先定义三个类，分别是实体类Employee.java，数据操作类EmployeeDao.java，业务逻辑类EmployeeService.java，下面是3个类的具体定义：

public class Employee {
    private String name;
    private Double salary;

    /**
     * @return the name
     */
    public String getName() {
        return name;
    }

    /**
     * @param name the name to set
     */
    public void setName(String name) {
        this.name = name;
    }

    /**
     * @return the salary
     */
    public Double getSalary() {
        return salary;
    }

    /**
     * @param salary the salary to set
     */
    public void setSalary(Double salary) {
        this.salary = salary;
    }

}

EmployeeDao.java：

public interface EmployeeDao {
    public Employee getEmployee(String name);

    public boolean updateEmployee(Employee employee);

    public static void deleteEmployee(String name) {
        throw new NullPointerException();
    }

    public Exception saveEmployee(Employee employee);
}

EmployeeService.java：

public class EmployeeServiceImpl {
    private EmployeeDao employeeDao;

    public EmployeeServiceImpl() {

    }

    public EmployeeServiceImpl(EmployeeDao employeeDao) {
        this.employeeDao = employeeDao;
    }

    public Employee getEmployee(String name) {
        return employeeDao.getEmployee(name);
    }

    public boolean updateEmployee(Employee employee) {
        return employeeDao.updateEmployee(employee);
    }

    public boolean deleteEmployee(String name) {
        try {
            EmployeeDao.deleteEmployee(name);
            return true;
        } catch (Exception e) {
            return false;
        }
    }

    public boolean saveEmployee(Employee employee) {
        try {
            employeeDao.saveEmployee(employee);
            return true;
        } catch (Exception e) {
            e.printStackTrace();
            return false;
        }
    }
}

下面是测试类中涉及到的PowerMockito知识点：

1）其中涉及到静态方法，因此需要使用@RunWith(PowerMockRunner.class)

@PrepareForTest({ EmployeeDao.class })注解，PrepareForTest的值是静态方法所在的类或接口，否则会报下面的错误：

org.powermock.api.mockito.ClassNotPreparedException: 
The class mock.EmployeeDao not prepared for test.
To prepare this class, add class to the '@PrepareForTest' annotation.
In case if you don't use this annotation, add the annotation on class or  method level. 

	at org.powermock.api.mockito.expectation.reporter.MockitoPowerMockReporter.classNotPrepared(MockitoPowerMockReporter.java:32)

2）使用@Before注解在调用@Test注解的方法之前进行初始化，比如使用mock(类的Class对象)来创建需要模拟的对象，这样我们就可以假设被模拟的对象已经实现，尽管他其实是一个没有实现类的接口。

3）在模拟对象创建之后，我们就可以使用when(调用模拟对象的方法).thenReturn(定义方法调用的返回值)，这样我们就相当于假设调用被模拟对象的方法后返回的一直是thenReturn中定义的值。这样我们就不用关心被模拟对象的实现按，只关心下面我们测试的业务逻辑是否存在问题。

@RunWith(PowerMockRunner.class)
@PrepareForTest({ EmployeeDao.class })
public class EmployeeServiceImplTest {
    @Mock
    public EmployeeDao employeeDao;

    @Mock
    EmployeeServiceImpl employeeServiceImpl;

    // @Before注解的方法会在调用测试方法前执行初始化动作
    @Before
    public void initMocks() {
        // 创建模拟对象EmployeeDao的实例
        employeeDao = mock(EmployeeDao.class);
        // 将模拟对象赋给业务类实例
        employeeServiceImpl = new EmployeeServiceImpl(employeeDao);
    }

    @Test
    public void getEmployeeTest() {
        String name = "scott";
        Employee employee = new Employee();
        employee.setName("scott");
        employee.setSalary(8888.0);
        // 定义当执行employeeDao.getEmployee(name)方法时始终返回employee对象，相当于实现了employeeDao的这个方法
        when(employeeDao.getEmployee(name)).thenReturn(employee);
        /*
         * 下面测试我们想要单元测试的employeeServiceImpl.getEmployee(name)方法 我们已经屏蔽了该方法对employeeDao.getEmployee(name)的调用，相当于解除了依赖
         * 这样我们只需要关心employeeServiceImpl.getEmployee(name)方法的逻辑是否存在问题
         */
        Employee employee2 = employeeServiceImpl.getEmployee(name);
        System.out.println(employee2.getSalary());
    }

    @Test
    public void updateEmployeeTest() {
        Employee employee = new Employee();
        employee.setName("tiger");
        employee.setSalary(99999.0);
        when(employeeDao.updateEmployee(anyObject())).thenReturn(true);
        Employee employee2 = new Employee();
        employee.setName("scott");
        employee.setSalary(99999.0);
        Boolean boolean1 = employeeServiceImpl.updateEmployee(employee2);
        System.out.println(boolean1);
    }

    @Test
    public void deleteEmployeeTest() {
        String name = "haha";
        // 因为这里调用的是静态方法，因此使用PowerMockito.mockStatic(EmployeeDao.class);来模拟静态类
        PowerMockito.mockStatic(EmployeeDao.class);
        // 使用doNothing()定义执行下面一句语句时什么也不做
        PowerMockito.doNothing().when(EmployeeDao.class);
        // 这一句由于上面的doNothing()即使会抛异常也不会再抛
        EmployeeDao.deleteEmployee(name);
        // 因此employeeServiceImpl.deleteEmployee(name)执行时也没有发现异常返回true
        EmployeeServiceImpl employeeServiceImpl = new EmployeeServiceImpl();
        Assert.assertTrue(employeeServiceImpl.deleteEmployee(name));
    }

    @Test
    public void throwDeleteExceptionTest() {
        String name = "haha";
        PowerMockito.mockStatic(EmployeeDao.class);
        // doThrow()定义下面一句语句会抛出异常
        PowerMockito.doThrow(new NullPointerException()).when(EmployeeDao.class);
        EmployeeDao.deleteEmployee(name);
        // 因此employeeServiceImpl.deleteEmployee(name)执行会返回false
        EmployeeServiceImpl employeeServiceImpl = new EmployeeServiceImpl();
        assertTrue(employeeServiceImpl.deleteEmployee(name));
    }

    @Test
    public void saveEmployeeTest() {
        Employee employee = new Employee();
        employee.setName("scott");
        employee.setSalary(8888.0);
        // 打桩，定义方法返回的值
        when(employeeDao.saveEmployee(employee)).thenReturn(new NullPointerException());
        // 这里doNothing()没有生效，原因是这里调用的是实例方法，不是静态方法
        PowerMockito.doNothing().when(employeeDao).saveEmployee(employee);
        employeeServiceImpl.saveEmployee(employee);
    }

    @Test
    public void throwSaveEmployeeTest() {
        Employee employee = new Employee();
        employee.setName("scott");
        employee.setSalary(8888.0);
        when(employeeDao.saveEmployee(employee)).thenReturn(new NullPointerException());
        // 这里的doThrow()实际没有生效，因为这里调用的是实例方法，不是静态方法，因此不存在使下一句语句抛异常的作用
        PowerMockito.doThrow(new NullPointerException()).when(employeeDao).saveEmployee(employee);
        employeeServiceImpl.saveEmployee(employee);
    }
}

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