This is a test piece for https://makerworld.com/en/models/178424#profileId-196305. You can use this to make sure your shelving is compliant with the model. Clips into place with a little bit of force and brackets do not move.

I listed it separately as it can be used to secure the hangar rod if you find one end is bending too much. See the picture attached to see how it can be used.