John Gill Commentary Exodus 16:34

"As Jehovah commanded Moses, so Aaron laid it up before the Testimony, to be kept." — Exodus 16:34 (ASV)

As the Lord commanded Moses, so Aaron laid it up before the testimony, to be kept. That is, before the ark of the testimony; when that was made, as it was in a little time after this, called the testimony, because it contained in it the law, which was a testimony or testification of the mind and will of God unto Israel, see (Exodus 25:16Exodus 25:21Exodus 25:22) the apostle says, the pot of manna was in the ark, (Hebrews 9:4) that is, on one side of it, (See Gill on Hebrews 9:4).