def test_iadd(self, evt):
        rval = event.ReturnValue(append_events=[evt])
        rval2 = event.ReturnValue(eat=True, append_events=[evt])
        rset = event.ResultSet()

        rset += rval
        rset += rval2
        rset += None
        assert rset.eat
        assert rset.append_events == [evt, evt]
def forcedens(title, pos, fdens, ax=0):
    """plot force densities"""
    if ax == 0:
        ax = plt.gca()
    ax.set_title(title)
    ax.grid(True)

    ax.plot(pos, [1e-3*ft for ft in fdens[0]], label='F tang')
    ax.plot(pos, [1e-3*fn for fn in fdens[1]], label='F norm')
    ax.legend()
    ax.set_xlabel('Pos / deg')
    ax.set_ylabel('Force Density / kN/m²')