Competence of husband and wife to give evidence as to cruelty or desertion.

On any petition presented, 6[by a husband or a wife, praying that his or her marriage may be dissolved by reason of his wife or her husband, as the case may be, having been guilty of adultery, cruelty or desertion], the husband and wife respectively shall be competent and compellable to give evidence of or relating to such cruelty or desertion.