test_FENE.py

from MPCDAnalysis.PairPotentials.FENE import FENE
 
def test_constructor_getK_get_l_0_getR():
    import pytest
 
    with pytest.raises(TypeError):
        FENE([1], 1, 1)
 
    with pytest.raises(TypeError):
        FENE(1, [1], 1)
 
    with pytest.raises(TypeError):
        FENE(1, 1, [1])
 
    with pytest.raises(ValueError):
        FENE(1, 1, 0)
 
    with pytest.raises(ValueError):
        FENE(1, 1, -1.5)
 
    fene = FENE(1, 2.5, 3)
 
 
    assert isinstance(fene.getK(), float)
    assert fene.getK() == 1.0
 
    assert isinstance(fene.get_l_0(), float)
    assert fene.get_l_0() == 2.5
 
    assert isinstance(fene.getR(), float)
    assert fene.getR() == 3.0
 
 
def test_getPotential():
    import math
    import pytest
 
    from MPCDAnalysis.Vector3DReal import Vector3DReal
 
    K = 2.0
    R = 10.0
    l_0 = 3.0
    fene = FENE(K, l_0, R)
 
    with pytest.raises(TypeError):
        fene.getPotential([1])
    with pytest.raises(ValueError):
        fene.getPotential(-1)
 
    with pytest.raises(ValueError):
        fene.getPotential(Vector3DReal(l_0 + R, 0, 0))
    with pytest.raises(ValueError):
        fene.getPotential(l_0 + R)
    with pytest.raises(ValueError):
        fene.getPotential(Vector3DReal(l_0 + R + 0.1, 0, 0))
    with pytest.raises(ValueError):
        fene.getPotential(l_0 + R + 0.1)
 
    r = Vector3DReal(0, 0, 0)
    expected = -0.5 * K * R * R * math.log(1 - (l_0 / R) ** 2)
    assert fene.getPotential(r) == expected
    assert fene.getPotential(r.getLength()) == expected
 
    for i in range(0, 100):
        r = Vector3DReal(-0.1 + i, i * 0.1, 2 * i)
        frac = (r.getLength() - l_0) / R
 
        if frac ** 2 >= 1:
            with pytest.raises(ValueError):
                fene.getPotential(r)
            continue
 
        expected = -0.5 * K * R * R * math.log(1 - frac ** 2);
        assert fene.getPotential(r) == expected
        assert fene.getPotential(r.getLength()) == expected