def test_hydrogens_given_invalid():
"""
Test that invalid atoms raise error when calling hydrogens.
"""
carb = AtomSpec(6, 4)
molecule = Molecule([carb], [])
with pytest.raises(ValueError):
molecule.hydrogens(1)
def test_hydrogens():
"""Test the number of virtual hydrogens."""
molecule = Molecule([AtomSpec('C')], [])
assert molecule.hydrogens(0) == 0
def test_hydrogens():
"""Test the number of hydrogens."""
molecule = Molecule([AtomSpec('C', 3, -1)], [])
assert molecule.hydrogens(0) == 3