def test_intsum():

    g = gen.intsum()

    assert g.next() == 0
    assert g.next() == 1
    assert g.next() == 3
    assert g.next() == 6
    assert g.next() == 10
    assert g.next() == 15
def test_intsum2():

    g = gen.intsum()

    assert next(g) == 0
    assert next(g) == 1
    assert next(g) == 3
    assert next(g) == 6
    assert next(g) == 10
    assert next(g) == 15