In an action by or against personal representatives, administrators, guardians or conservators in which judgment may be given for or against them as such, neither party shall be allowed to testify against the other as to any transaction with or statement by the testator, intestate or ward unless called to testify thereto by the opposite party, or required to testify thereto by the court. The provisions of this section shall extend to and include all actions by or against the heirs, devisees, legatees or legal representatives of a decedent arising out of any transaction with the decedent.