<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC
 "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
 "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
    <session-factory>
        <!-- Database connection settings -->
        <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
        <property name="connection.url">jdbc:mysql://localhost/UserDB</property>
        <property name="connection.username">root</property>
        <property name="connection.password"></property>

        <!-- JDBC connection pool (use the built-in) -->
        <property name="connection.pool_size">1</property>

        <!-- SQL dialect -->
        <property name="dialect">org.hibernate.dialect.MySQL5Dialect</property>

        <!-- Enable Hibernate's automatic session context management -->
        <property name="current_session_context_class">thread</property>

        <!-- Disable the second-level cache -->
        <property name="cache.provider_class">org.hibernate.cache.NoCacheProvider</property>

        <!-- Echo all executed SQL to stdout -->
        <property name="show_sql">true</property>
        <property name="format_sql">true</property>

        <!-- Drop and re-create the database schema on startup -->
        <property name="hbm2ddl.auto">create</property>

        <!-- Mapping files -->
        <mapping class="com.stackoverflow.model.Student" />
        <mapping class="com.stackoverflow.model.School" />

    </session-factory>
</hibernate-configuration>

public class TestDao {

    private static SessionFactory sessionFactory;
    private Session session;

    @BeforeClass
    public static void setUp() throws Exception {
        // A SessionFactory is set up once for an application!
        final StandardServiceRegistry registry = new StandardServiceRegistryBuilder()
                .configure("hibernate.cfg.xml") // configures settings from hibernate.cfg.xml
                .build();
        try {
            sessionFactory = new MetadataSources( registry ).buildMetadata().buildSessionFactory();
        }
        catch (Exception e) {
            // The registry would be destroyed by the SessionFactory, but we had trouble building the SessionFactory
            // so destroy it manually.
            StandardServiceRegistryBuilder.destroy( registry );
        }
        assertNotNull(sessionFactory);
    }

    @AfterClass
    public static void tearDown() throws Exception {
        sessionFactory.close();
    }

    @Before
    public void beforeEach() {
        session = sessionFactory.openSession();
        session.beginTransaction();

    }
    @After
    public void afterEach() {
        session.getTransaction().commit();
        session.close();
    }

    @Test
    public void testSave() {
        School school= new School("Ivanofrankivsk, Myk town, We str");
        Student student1 = new Student("student1",LocalDate.of(1988, 8, 12),school);
        Student student2 = new Student("student2",LocalDate.of(1977, 2, 1),school);
        Student student3 = new Student("student3",LocalDate.of(1999, 1, 1),school);

        school.addStudent(student1);
        school.addStudent(student2);
        school.addStudent(student3);

        session.save(school);
    }
}

java.lang.AssertionError: null
    at org.junit.Assert.fail(Assert.java:86)
    at org.junit.Assert.assertTrue(Assert.java:41)
    at org.junit.Assert.assertNotNull(Assert.java:621)
    at org.junit.Assert.assertNotNull(Assert.java:631)
    at com.stackoverflow.dao.TestDao.setUp(TestDao.java:47)