test_WeeksChandlerAndersen_DistanceOffset.py

from MPCDAnalysis.PairPotentials.WeeksChandlerAndersen_DistanceOffset \
    import WeeksChandlerAndersen_DistanceOffset as WCAD
 
def test_constructor_get_parameters():
    import pytest
 
    with pytest.raises(TypeError):
        WCAD([1], 1, 1)
 
    with pytest.raises(TypeError):
        WCAD(1, [1], 1)
 
    with pytest.raises(TypeError):
        WCAD(1, 1, [1])
 
 
    with pytest.raises(ValueError):
        WCAD(-1, 0.1, 2.3)
 
    with pytest.raises(ValueError):
        WCAD(1, -0.1, 2.3)
 
    with pytest.raises(ValueError):
        WCAD(1, 0.1, -2.3)
 
 
    pot = WCAD(1, 2.5, 3)
 
 
    assert isinstance(pot.getEpsilon(), float)
    assert pot.getEpsilon() == 1.0
 
    assert isinstance(pot.getSigma(), float)
    assert pot.getSigma() == 2.5
 
    assert isinstance(pot.getD(), float)
    assert pot.getD() == 3.0
 
 
def test_getPotential():
    import pytest
 
    from MPCDAnalysis.Vector3DReal import Vector3DReal
 
    epsilon = 10.0
    sigma = 2.0
    d = 1.2
    pot = WCAD(epsilon, sigma, d)
 
    def expected(r):
        if isinstance(r, Vector3DReal):
            r = r.getLength()
 
        if r <= d:
            return None
 
        ret = 0.0
        if 2 ** (1.0 / 6.0) * sigma - r + d > 0:
            frac = sigma / (r - d)
            ret = 1.0 / 4.0
            ret += frac ** 12
            ret -= frac ** 6
            ret *= 4 * epsilon
 
        return ret
 
 
    with pytest.raises(TypeError):
        pot.getPotential([1])
    with pytest.raises(ValueError):
        pot.getPotential(-1)
 
    r = Vector3DReal(0, 0, 0)
    with pytest.raises(ValueError):
        pot.getPotential(r)
    with pytest.raises(ValueError):
        pot.getPotential(r.getLength())
 
    for i in range(0, 100):
        r = Vector3DReal(-0.1 + i, i * 0.1, 2 * i)
 
        e = expected(r)
        if e is None:
            with pytest.raises(ValueError):
                pot.getPotential(r)
            continue
 
        assert pot.getPotential(r) == pytest.approx(e)
        assert pot.getPotential(r.getLength()) == pytest.approx(e)