def test_vasp_co(require_vasp):
    """
    Run some VASP tests to ensure that the VASP calculator works. This
    is conditional on the existence of the VASP_COMMAND or VASP_SCRIPT
    environment variables

    """

    from ase.test.calculator.vasp import installed

    assert installed()

    from ase import Atoms
    from ase.io import write
    from ase.calculators.vasp import Vasp
    import numpy as np

    def array_almost_equal(a1, a2, tol=np.finfo(type(1.0)).eps):
        """Replacement for old numpy.testing.utils.array_almost_equal."""
        return (np.abs(a1 - a2) < tol).all()

    d = 1.14
    co = Atoms('CO', positions=[(0, 0, 0), (0, 0, d)],
                  pbc=True)
    co.center(vacuum=5.)

    calc = Vasp(
                xc = 'PBE',
                prec = 'Low',
                algo = 'Fast',
                ismear= 0,
                sigma = 1.,
                istart = 0,
                lwave = False,
                lcharg = False)

    co.calc = calc
    en = co.get_potential_energy()
    write('vasp_co.traj', co)
    assert abs(en + 14.918933) < 5e-3

    # Secondly, check that restart from the previously created VASP output works

    calc2 = Vasp(restart=True)
    co2 = calc2.get_atoms()

    # Need tolerance of 1e-14 because VASP itself changes coordinates
    # slightly between reading POSCAR and writing CONTCAR even if no ionic
    # steps are made.
    assert array_almost_equal(co.positions, co2.positions, 1e-14)

    assert en - co2.get_potential_energy() == 0.
    assert array_almost_equal(calc.get_stress(co), calc2.get_stress(co2))
    assert array_almost_equal(calc.get_forces(co), calc2.get_forces(co2))
    assert array_almost_equal(calc.get_eigenvalues(), calc2.get_eigenvalues())
    assert calc.get_number_of_bands() == calc2.get_number_of_bands()
    assert calc.get_xc_functional() == calc2.get_xc_functional()

    # Cleanup
    calc.clean()
