OK. In this case I found a way to rewrite the assert so that test case is simpler:
def test_O4():
    (ex,ey,ez,grad) = MV.setup('e*x|y|z',metric='[1,1,1]',coords=(x,y,z))
    F=ex*(x*y*z)+ey*((x*y*z)**2)+ez*((y**2)*(z**3))
    assert grad^F -(x*z*(2*y**2*z - 1))*ex^ey - x*y*ex^ez + (2*y*z*(-x**2*y + z**2))*ey^ez == 0