Testing function with stdin and stdout

test.py

from io import StringIO


def adding():
    x = int(input('Anna luku 1'))
    y = int(input('Anna luku 2'))
    print("Summa on %d" % (x + y))


def test_adding(monkeypatch, capsys):
    number_inputs = StringIO('2\n3\n')
    monkeypatch.setattr('sys.stdin', number_inputs)
    adding()
    captured = capsys.readouterr()
    assert "Summa on 5" in captured.out