@BeforeClass
public static void setUpJdbc() throws IOException, InterruptedException, SQLException {
        Connection c = DriverManager.getConnection("jdbc:postgresql://localhost:5432/default_db", "user_name", "pw");
        Statement statement = c.createStatement();
        statement.executeUpdate("create database test_db with template test_template;");
        statement.close();
        c.close();
    }

@AfterClass
public static void tearDownJdbc() throws SQLException {
            Connection c = DriverManager.getConnection("jdbc:postgresql://localhost:5432/default_db", "user_name", "pw");
            Statement statement = c.createStatement();
            statement.executeUpdate("REVOKE CONNECT ON DATABASE test_db FROM public;");
            statement.execute("SELECT pid, pg_terminate_backend(pid) n" +
                    "FROM pg_stat_activity n" +
                    "WHERE datname = 'test_db' AND pid <> pg_backend_pid();");
            statement.executeUpdate("drop database if exists test_db;");
            statement.close();
            c.close();
    }

public List<Object> query(String sqlquery) throws DatabaseConnectionException {
    Session session = null;
    Transaction transcation = null;
    List<Object> sqlQueryResults = null;
    try {
        session = factory.openSession();
        transcation = session.beginTransaction();
        Query query = session.createNativeQuery(sqlquery);
        sqlQueryResults = query.list();
        transcation.commit();
    } catch (SQLGrammarException e) {
        if (transcation != null)
            transcation.rollback();
        throw new DatabaseConnectionException();
    } catch (HibernateException e) {
        if (transcation != null)
            transcation.rollback();
        throw new DatabaseConnectionException();
    } finally {
        if (session != null)
            session.close();
    }
    return sqlQueryResults;
}

org.hibernate.exception.JDBCConnectionException: Unable to release JDBC Connection
    at org.hibernate.exception.internal.SQLStateConversionDelegate.convert(SQLStateConversionDelegate.java:115)
    at org.hibernate.exception.internal.StandardSQLExceptionConverter.convert(StandardSQLExceptionConverter.java:42)
    at org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlExceptionHelper.java:111)
    at org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlExceptionHelper.java:97)
    at org.hibernate.resource.jdbc.internal.LogicalConnectionManagedImpl.releaseConnection(LogicalConnectionManagedImpl.java:199)
    at org.hibernate.resource.jdbc.internal.LogicalConnectionManagedImpl.close(LogicalConnectionManagedImpl.java:239)
    at org.hibernate.engine.jdbc.internal.JdbcCoordinatorImpl.close(JdbcCoordinatorImpl.java:189)
    at org.hibernate.internal.AbstractSharedSessionContract.close(AbstractSharedSessionContract.java:311)
    at org.hibernate.internal.SessionImpl.close(SessionImpl.java:423)
    at com.dummy.DataLayer.query(DataLayer.java:173)
    at com.dummy.MITypeCompositeDAO.getLatestExecutionForUser(MITypeCompositeDAO.java:71)
    at com.dummy.MITypeCompositeDAO.getMITypeCompositeForUser(MITypeCompositeDAO.java:137)
    at com.dummy.MITypeCompositeDAOTest.testGetMITypeCompositeForUser(MITypeCompositeDAOTest.java:62)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:44)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:41)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:20)
    at org.junit.runners.BlockJUnit4ClassRunner.runNotIgnored(BlockJUnit4ClassRunner.java:79)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:71)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:49)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:193)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:52)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:191)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:42)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:184)
    at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:28)
    at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:31)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:236)
    at org.apache.maven.surefire.junit4.JUnit4Provider.execute(JUnit4Provider.java:369)
    at org.apache.maven.surefire.junit4.JUnit4Provider.executeWithRerun(JUnit4Provider.java:275)
    at org.apache.maven.surefire.junit4.JUnit4Provider.executeTestSet(JUnit4Provider.java:239)
    at org.apache.maven.surefire.junit4.JUnit4Provider.invoke(JUnit4Provider.java:160)
    at org.apache.maven.surefire.booter.ForkedBooter.invokeProviderInSameClassLoader(ForkedBooter.java:373)
    at org.apache.maven.surefire.booter.ForkedBooter.runSuitesInProcess(ForkedBooter.java:334)
    at org.apache.maven.surefire.booter.ForkedBooter.execute(ForkedBooter.java:119)
    at org.apache.maven.surefire.booter.ForkedBooter.main(ForkedBooter.java:407)
Caused by: org.postgresql.util.PSQLException: This connection has been closed.
    at org.postgresql.jdbc.PgConnection.checkClosed(PgConnection.java:766)
    at org.postgresql.jdbc.PgConnection.setAutoCommit(PgConnection.java:712)
    at org.hibernate.engine.jdbc.connections.internal.PooledConnections.add(PooledConnections.java:68)
    at org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl.closeConnection(DriverManagerConnectionProviderImpl.java:195)
    at org.hibernate.internal.NonContextualJdbcConnectionAccess.releaseConnection(NonContextualJdbcConnectionAccess.java:46)
    at org.hibernate.resource.jdbc.internal.LogicalConnectionManagedImpl.releaseConnection(LogicalConnectionManagedImpl.java:196)
    ... 35 more