Mockito在JUnit测试中的使用

Mockito是一种用于替代在测试中难以实现的成员，从而让testcase能顺利覆盖到目标代码的手段。下面例子将展示Mockito的使用。

完整代码下载：https://files.cnblogs.com/files/xiandedanteng/mockitoTest20200311.zip

首先有这么一个需要测试的类：

package mockito;

public class EmpService {
    private EmpDao dao;
    
    public EmpService() {
        dao=new EmpDao();
    }
    
    public boolean isWeakPswd(long empId) {
        // roadlock which hinder running bacause of no environment
        Emp emp=dao.getById(empId);
        
        // Real code need to be tested,but unreachable because emp is null
        if(emp.getPswd().equals("111111")) {
            return true;
        }else if(emp.getPswd().equals("123456")) {
            return true;
        }else if(emp.getName().equals(emp.getPswd())) {
            return true;
        }else {
            return false;
        }
    }
}

其中isWeakPswd是需要测试的方法，但问题是dao不能在测试环境中就绪，因此跑不到下面的if语句。

package mockito;

public class EmpDao {
    public Emp getById(long id) {
        // Access auth/redis/db to get a real emp,but it is difficult to set up environment in test,so return null
        return null;
    }
}

EmpDao的getById方法不能就绪的原因是需要搭建完整的认证/redis/db环境，总之搞不成就是了。大家在测试某些类也会发生内部的mapper，dao不能就绪的情况，这和本例情况类似。

然后下面的测试方法就走不下去了，因为一跑isWeakPswd方法就会抛出空指针异常；

    @Test
    public void normalTestWeakPswd() {
        EmpService service=new EmpService();
        
        // NullPointerException will be thrown out and case will fail
        boolean actual=service.isWeakPswd(10001);
        
        Assert.assertSame(true, actual);
    }

 然后怎么办呢？任凭Coverrage在低位徘徊？当然不是，这个时候就该请Mock出场了。

Mock本身就是个空壳，作用是替代无法就绪的对象，达到测试其后代码的目的。下面就制作了mockDao用来替代EmpService里的empDao

    @Test
    public void testWeakPswd_ByMock_01() throws Exception {
        EmpDao mockDao = Mockito.mock(EmpDao.class); // 创建
        Emp emp=new Emp(10001,"Andy","111111");      // 返回值
        Mockito.when(mockDao.getById(10001)).thenReturn(emp);// 设置调用getById时返回固定值
        
        // Use reflection replace dao with mockDao，利用反射用mock对象取代原有的empDao
        EmpService service=new EmpService();
        Field daoField = service.getClass().getDeclaredField("dao");
        daoField.setAccessible(true);
        daoField.set(service, mockDao);
        
        Assert.assertEquals(true, service.isWeakPswd(10001));// 这样，isWeakPswd方法就不会抛出空指针异常了
    }

这样，Mock对象就当好了替补队员的角色，使得isWeakPswd的代码可以达到了。

Mockito的使用就这样简单，无非是创建，设定要模拟的函数的返回值（或异常），然后用反射方法进行顶替三部曲，下面是测试类的全部代码：

package mockitoTest;

import java.lang.reflect.Field;

import org.junit.Assert;
import org.junit.Before;
import org.junit.Rule;
import org.junit.Test;
import org.junit.rules.ExpectedException;
import org.mockito.Mockito;

import mockito.Emp;
import mockito.EmpDao;
import mockito.EmpService;

public class EmpServiceTest {
    @Rule
    public ExpectedException exception = ExpectedException.none(); // No Exception thrown Allowed
    
    private EmpDao memberMockDao;
    
    @Before
    public void init() throws Exception {
        memberMockDao = Mockito.mock(EmpDao.class);
        Emp emp=new Emp(10002,"Bill","123456");
        Mockito.when(memberMockDao.getById(10002)).thenReturn(emp);
    }
    
    @Test
    public void normalTestWeakPswd() {
        EmpService service=new EmpService();
        
        // NullPointerException will be thrown out and case will fail
        boolean actual=service.isWeakPswd(10001);
        
        Assert.assertSame(true, actual);
    }
    
    @Test
    public void testWeakPswd_ByMock_01() throws Exception {
        EmpDao mockDao = Mockito.mock(EmpDao.class);
        Emp emp=new Emp(10001,"Andy","111111");
        Mockito.when(mockDao.getById(10001)).thenReturn(emp);
        
        // Use reflection replace dao with mockDao
        EmpService service=new EmpService();
        Field daoField = service.getClass().getDeclaredField("dao");
        daoField.setAccessible(true);
        daoField.set(service, mockDao);
        
        Assert.assertEquals(true, service.isWeakPswd(10001));
    }
    
    @Test
    public void testWeakPswd_ByMock_02() throws Exception {
    
        // Use reflection replace dao with mockDao
        EmpService service=new EmpService();
        Field daoField = service.getClass().getDeclaredField("dao");
        daoField.setAccessible(true);
        daoField.set(service, memberMockDao);
        
        Assert.assertEquals(true, service.isWeakPswd(10002));
    }
    
    @Test
    public void testWeakPswd_ByMock_03() throws Exception {
        EmpDao mockDao = Mockito.mock(EmpDao.class);
        Emp emp=new Emp(10003,"Cindy","Cindy");
        Mockito.when(mockDao.getById(10003)).thenReturn(emp);
        
        // Use reflection replace dao with mockDao
        EmpService service=new EmpService();
        Field daoField = service.getClass().getDeclaredField("dao");
        daoField.setAccessible(true);
        daoField.set(service, mockDao);
        
        Assert.assertEquals(true, service.isWeakPswd(10003));
    }
}

要测试的EmpService类：

package mockito;

public class EmpService {
    private EmpDao dao;
    
    public EmpService() {
        dao=new EmpDao();
    }
    
    public boolean isWeakPswd(long empId) {
        // roadlock which hinder running bacause of no environment
        Emp emp=dao.getById(empId);
        
        // Real code need to be test,but unreachable because emp is null
        if(emp.getPswd().equals("111111")) {
            return true;
        }else if(emp.getPswd().equals("123456")) {
            return true;
        }else if(emp.getName().equals(emp.getPswd())) {
            return true;
        }else {
            return false;
        }
    }
}

因伤不能上阵的EmpDao类：

package mockito;

public class EmpDao {
    public Emp getById(long id) {
        // Access auth/redis/db to get a real emp,but it is difficult to set up environment in test,so return null
        return null;
    }
}

实体类Emp：

package mockito;

public class Emp {
    private long id;
    private String name;
    private String pswd;
    
    public Emp() {
        
    }
    
    public Emp(long id,String name,String pswd) {
        this.id=id;
        this.name=name;
        this.pswd=pswd;
    }

    public long getId() {
        return id;
    }

    public void setId(long id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getPswd() {
        return pswd;
    }

    public void setPswd(String pswd) {
        this.pswd = pswd;
    }
}

要使用Mockito，可以在pom.xml里进行如以下红字部分设置：

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>com</groupId>
  <artifactId>logbackCfg</artifactId>
  <version>0.0.1-SNAPSHOT</version>

    <properties>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>ch.qos.logback</groupId>
            <artifactId>logback-classic</artifactId>
            <version>1.1.11</version>
        </dependency>
        
        <dependency>
            <groupId>ch.qos.logback</groupId>
            <artifactId>logback-core</artifactId>
            <version>1.1.11</version>
        </dependency>
        
        <dependency>
            <groupId>org.mockito</groupId>
            <artifactId>mockito-core</artifactId>
            <version>3.1.0</version>
            <scope>test</scope>
        </dependency>
        
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
            <scope>test</scope>
        </dependency>
    </dependencies>
</project>

--2020年3月11日--

参考资料：http://www.voidcn.com/article/p-vekqzrow-btm.html

Mock与反射关系不小，这里是反射资料：https://blog.csdn.net/a745233700/article/details/82893076

反射资料2：https://www.sczyh30.com/posts/Java/java-reflection-1/