Engineering test bay alpha was a section of engineering on the Crossfield-class starship USS Discovery. A standard engineering workspace specially converted to accommodate the spore drive, it housed the reaction cube, mycelium spore storage canisters, and a secured passageway to an adjacent cultivation bay where Paul Stamets grew his spores. (DIS: "Context Is for Kings", "Brother")
In 2257, after Discovery encountered an unknown lifeform, Jett Reno was sent to secure this section of the ship. (DIS: "An Obol for Charon")
A zoom out near the end of "Context Is for Kings" shows the lab to be located in the secondary hull, just to the left of the ship's "spine".
The spore drive room aboard USS Glenn
had the same design.