要測試MyBatis中定義的typeAlias，你需要遵循以下步驟：

1. 添加依賴：確保你的項目中已經添加了MyBatis和相關數據庫驅動的依賴。

2. 配置MyBatis：創建一個mybatis-config.xml文件，配置typeAlias。例如：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "http://mybatis.org/dtd/mybatis-3-config.dtd"><configuration>
    <typeAliases>
        <typeAlias type="com.example.model.User" alias="User"/>
    </typeAliases>
</configuration>

3. 創建實體類：根據typeAlias的配置，創建對應的實體類。例如，創建一個User類：

package com.example.model;

public class User {
    private int id;
    private String name;
    // getter and setter methods
}

4. 創建Mapper接口：創建一個Mapper接口，用于操作數據庫。例如，創建一個UserMapper接口：

package com.example.mapper;

import com.example.model.User;

public interface UserMapper {
    User getUserById(int id);
}

5. 創建Mapper XML文件：為Mapper接口創建一個XML文件，用于編寫SQL語句。例如，創建一個UserMapper.xml文件：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.example.mapper.UserMapper">
   <select id="getUserById" resultType="User">
        SELECT * FROM user WHERE id = #{id}
    </select>
</mapper>

6. 編寫測試用例：使用JUnit或其他測試框架編寫測試用例，測試typeAlias是否正常工作。例如：

package com.example.test;

import com.example.mapper.UserMapper;
import com.example.model.User;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.BeforeClass;
import org.junit.Test;

import java.io.InputStream;

import static org.junit.Assert.*;

public class TypeAliasTest {
    private static SqlSessionFactory sqlSessionFactory;

    @BeforeClass
    public static void setUp() throws Exception {
        InputStream inputStream = Resources.getResourceAsStream("mybatis-config.xml");
        sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
    }

    @Test
    public void testTypeAlias() {
        try (SqlSession sqlSession = sqlSessionFactory.openSession()) {
            UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
            User user = userMapper.getUserById(1);
            assertNotNull(user);
            assertEquals(1, user.getId());
        }
    }
}

7. 運行測試用例：運行測試用例，如果測試通過，說明typeAlias配置正確，可以正常工作。如果測試失敗，檢查配置和代碼是否有誤。