@User, just fyi, the test_comparator needs a stimuli file,

stimuli.test_comparator

, copy this file from the xschem_sky130/sky130_tests/ to ~/.xschem/simulations, on my system:

cp ~/.xschem/xschem_library/xschem_sky130/sky130_tests/stimuli.test_comparator ~/.xschem/simulations/

then before launching simulation, in xschem, in the test_comparator schematic:

simulation->Utile stimuli editor(GUI)

, press 'Translate', 'Dismiss'. This creates a spice pwl stimuli file,

stimuli_test_comparator.cir

, needed for the ngspice simulation.