def test_normality():
    X, Y = Normal('X', 0, 1), Normal('Y', 0, 1)
    x, z = symbols('x, z', real=True, finite=True)
    dens = density(X - Y, Eq(X + Y, z))

    assert integrate(dens(x), (x, -oo, oo)) == 1
dataset/ETHPy150Open sympy/sympy/sympy/stats/tests/test_rv.py/test_normality/original