repository관련 질문

repository 코드입니다.

private static long sequence = 0L;
private DataSource dataSource;

public DbMemberRepository(DataSource dataSource) {
    this.dataSource = dataSource;
}

public void save(String memberId, String password) throws SQLException {
    String sql = "insert into member(id, member_id, password) values(?,?,?)";


    try {
        Connection con = null;
        PreparedStatement pstmt;
        con = getConnection();
        pstmt = con.prepareStatement(sql);
        pstmt.setLong(1, ++sequence);
        pstmt.setString(2, memberId);
        pstmt.setString(3, password);

        log.info(String.valueOf(sequence));


        pstmt.execute();
    } catch (SQLException e) {
        throw new SQLException("sql exception");
    }

}

@Test
void save() throws SQLException {
    memberRepository.save("test1", "test1!");
    //memberRepository.save("test2", "test2!");
}

 위 코드에서 save테스트를 돌릴 때 save test를 두번 누르면 sequence(id)가 1, 2로 저장된다고 생각했는데 에러가 나고 test코드내에서 memberRepository.save를 두번적으면 되더라고요. 왜 전자처럼 두번누르는 것은 예외가 나나요?