def test_isotope_given_invalid():
"""
Test that invalid atoms raise error when calling isotope.
"""
carb = AtomSpec(6, 4)
molecule = Molecule([carb], [])
with pytest.raises(ValueError):
molecule.isotope(1)
def test_hyd_deut():
"""Test that isotopes are set correctly."""
hyd = AtomSpec('H', isotope=1)
deut = AtomSpec(1, isotope=2)
molecule = Molecule([hyd, deut], [BondSpec(0, 1, 1)])
assert molecule.isotope(0) == 1
assert molecule.isotope(1) == 2