When a witness whose testimony is necessary to be used before any probate court shall reside out of this State or out of the county where the court is held or more than thirty miles from the county seat, or when by reason of age or bodily infirmity any such witness shall be unable to attend in person, the court may issue a commission to one or more competent persons to take the testimony of such witness. Depositions taken according to the provisions of the law for taking depositions to be used on the trial of civil causes may be used on the trial of any question before the probate court when such testimony may be proper.