If, after a petition for the probate of a will has been filed, another instrument in writing purporting to be the last will or codicil shall be presented, proceedings shall be had for the probate thereof and thereupon the hearing on the petition theretofore filed shall be adjourned to the time fixed for the hearing of the subsequent petition. At such time proof shall be had upon all of such wills, codicils, and all matters pertaining thereto, and the court shall determine which of such instruments, if any, should be allowed as the last will.