internal/core/adt: add tests for 3967
Issue #3967
Signed-off-by: Marcel van Lohuizen <mpvl@gmail.com>
Change-Id: I67807947ff65936f92bab9b54d5385d6b1392f33
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1217085
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: CUEcueckoo <cueckoo@cuelang.org>
Unity-Result: CUE porcuepine <cue.porcuepine@gmail.com>