nosetest a function with random elements

Question

Hi I am new to unit tests and was wondering how I would test a function that has a random component in it?

I have the following python code:

class Questions(object):

def __init__(self):

    self.questions = {}

place_value = {
    0: "Thousands",
    1: "Hundreads",
    2: "Tens",
    3: "Units/ones",
}

def place_value(self, question, number):

    selection = randint(0, 3)

    number = ''.join(map(str, number))
    value = number[selection]

    question_text = question.format(value, number)

    li = generate_a_list(question_text)

    self.questions['question1'] = li

test code

def test_place_value():

    obj = math_q.Questions()
    obj.place_value("value of {0} in {1}", [1,2,3,4])

    assert_equal(obj.questions["question1"], ["value of {0} in 1234"])

The problem being I don't know which value 1-4 is selected from the 'value = number[selection]' code above.

What can be done about this? Thanks.

Answer 1

Assuming your code is in path/my_file.py you can use mock module like this:

@mock.patch('path.my_file.randint', return_value=0)
def test_place_value(m_randint):
    obj = math_q.Questions()
    obj.place_value("value of {0} in {1}", [1,2,3,4])

    m_randint.assert_called_once_with(0, 3)
    assert obj.questions["question1"] == ...

Then just write 4 tests to handle all cases.

Side note: I strongly suggest switching to pytest.