But that's the OT, right? Testament means Covenant, and vise versa.
Hebrews 9:16-17 For where there is a testament, there must also of necessity be the death of the testator. For a testament is in force after men are dead, since it has no power at all while the testator lives.
Jesus was recorded crucified in John chapter 19. So John chapter 3 is still the Old Testament. Since Jesus rose from the dead, His covenant/Testament is a permanent one.
It's constructed from Scripture, not tradition.
See John 3:13