Godot's AnimationPlayer is built to run one animation at a time, which can be blended with one other animation at a time. That's what custom_blend is for. When you do
AnimationPlayer.play("test", 1, 1)
it will blend from the last animation to the new one. If you repeat this, it will ignore the very first animation, because only two can be blended.
If you want to have multiple animations running simultaneously, use multiple players or AnimationTreePlayer.