All the allegations of the petition must be verified by oath and proved by competent evidence. No divorce shall be granted on the evidence of the applicant alone, and all such actions shall be heard in open court on the testimony of witnesses or depositions. [Sec.3413.] No divorce can be granted by consent of parties unless grounds therefor can be shown by competent evidence, and if collusion or conrivance on the part of the defendant can be shown, such fact will be a valid defense.