CODEWITHSUNDEEP
pythonunit-testing
Muhammad Lukman Low
Muhammad Lukman Low

Reputation: 8533

How do you get to the value inside of a python function that returns nothing for unit testing?

I am trying to write a unit test for an existing function:

def _fetch_law(self, task, storage):
    number, link = task
    if not self.silent:
        print 'Requesting page %s' % number
    r = requests.get(link, headers=self.headers)

    if r.status_code != 200:
        sys.exit('CONNECTION ERROR!!! HTTP ERROR %d' % r.status_code)
    vs = LawPages(r.text)
    storage.extend(vs.extract())

For my unit testing, how do I use mocking or other means to get to the final value that is passed to storage ?

Upvotes: 0

Views: 99

Answers (3)

Brian Pendleton
Brian Pendleton

Reputation: 829

Lawrence is correct, just do something simple like:

def test_fetch_law():
    store = []
    task = ...
    cls = ClassWithFetchLaw()
    cls._fetch_law(task, store)
    assert len(store) > 0

On another note, if you're going down the unit test route, why not have the sys.exit throw an exception and write another test for it? Unless you really want the sys.exit in there...

def test_fetch_law_throws():
    store = []
    bad_task = ...
    cls = ClassWithFetchLaw()
    with pytest.raises(Exception):
        cls._fetch_law(bad_task, store)

Upvotes: 0

mgilson
mgilson

Reputation: 310099

I generally use the mock library (unittest.mock in python3.x). It would look something like:

mock_storage = mock.Mock()
obj._fetch_law(some_task, mock_storage)
mock_storage.extend.assert_called_with(expected_value)

Of course, in this example, you might want to mock out requests as well... mock.patch is great for that:

with mock.patch.object(requests, 'get') as mock_get:
    mock_get.return_value = ' ... '
    mock_storage = mock.Mock()
    obj._fetch_law(some_task, mock_storage)
    mock_storage.extend.assert_called_with(expected_value)

Upvotes: 0

Lawrence Benson
Lawrence Benson

Reputation: 1406

As you are passing storage to the function, why don't you just create an empty list which you pass on. The function will append to storage and you can then check, what is in that list and if it is the expected result.

Upvotes: 2

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