How to parameterize a non-deterministic function in pytest?

Question

Say I have a function which returns a random item from a list:

def get_item(L):
    if not L: return None
    return random.choice(L)

How can I use parameterization with pytest to test both cases?

Answer 1

You can easily pass in parameters which give a deterministic result:

result = get_item(None)
assert result is None

result = get_item([42])
assert result == 42

random.seed(1)
result = get_item([1,2,3])
assert result == 1