Light can pass through test instance blocks

Light passes through test instance blocks.

How to reproduce:

1. On the surface, during daytime, enclose yourself in a single layer of solid blocks, so that there is no light at your position.
2. Replace one of the enclosure's blocks with a test instance block.
   → The sun now lights the inside of the enclosure.

Expected result:

Light wouldn't be able to pass through test instance blocks.

Observed result:

Light can pass through test instance blocks.