def test_spin_z(orbitals, mapping, terms_exp, monkeypatch):
r"""Tests the correctness of the :math:`\hat{S}_z` observable built by the
function `'spin_z'`.
The parametrized inputs are `.terms` attribute of the `QubitOperator. The equality
checking is implemented in the `qchem` module itself as it could be something
useful to the users as well.
"""
Sz = qchem.spin_z(orbitals, mapping=mapping)
Sz_qubit_op = QubitOperator()
monkeypatch.setattr(Sz_qubit_op, "terms", terms_exp)
assert qchem._qubit_operators_equivalent(Sz_qubit_op, Sz)
def test_exception_spin_z(orbitals, msg_match):
"""Test that the function `'spin_z'` throws an exception if the
number of orbitals is less than zero."""
with pytest.raises(ValueError, match=msg_match):
qchem.spin_z(orbitals)