internal/core/adt: add tests for 3832

Issue #3832

Signed-off-by: Marcel van Lohuizen <[email protected]>
Change-Id: Id753868378bc7921ff13a104639b560a3831bb07
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1211844
Reviewed-by: Daniel Martí <[email protected]>
TryBot-Result: CUEcueckoo <[email protected]>
Unity-Result: CUE porcuepine <[email protected]>

Author: mpvl