Boyd’s Bible Dictionary:
As the stone tables of the Ten Commandments were called the “tables of testimony”
(Ex. 31:18; 32:15; 34:29); and the ark which contained them was called the “ark of testimony” (Ex. 25:22), so the tabernacle in which the ark was placed was called the “tabernacle of testimony” (Ex. 38:21; Num. 1:50). Called also “the tabernacle of witness” (Num. 17:7-8).