In all civil cases it shall be good cause of challenge that a juror has expressed an opinion as to which party ought to prevail or that he has a wish or desire as to which shall succeed. Upon challenge made by either party upon either of these grounds, it shall be the duty of the court to hear the competent evidence respecting the challenge as shall be submitted by either party, the juror being a competent witness. The court shall determine the challenge according to the opinion it entertains of the evidence adduced thereon.