import sys

from ase import Atoms
from ase.io import write
from ase.test import cli


write('x.json', Atoms('X'))

# Make sure ASE's gui can run in terminal mode without $DISPLAY and tkinter:
cli('ase -T gui --terminal x.json@id=1')
assert 'tkinter' not in sys.modules
assert 'Tkinter' not in sys.modules  # legacy Python