If a testament only goes into effect after the death of the testator, then who died to authorize the effect of the Old Testament (Heb. 9:16-17)?

Hebrews 9:16-17 was referenced in the question.  Let’s examine the verses which follow.  In them the writer of Hebrews shows that the first covenant – the Old Testament – was inaugurated with the blood of animals (9:18-22).  He then wrote of how this was a copy, or foreshadowing, of the greater and better spiritual truths of the New Testament (Heb. 9:23-10:1).

Thus, Moses’ law did require death, the death of animals.  However, it was meant to be a type or shadow of the complete salvation offered to man in the New Testament through Christ’s death.  This was to show the superiority of the New Testament, in that animals’ deaths could not forgive sins as Christ’s death did.