unit testing - How to mock a redis client in Python?

Question

I just found that a bunch of unit tests are failing, due a developer hasn't mocked out the dependency to a redis client within the test. I'm trying to give a hand in this matter but have difficulties myself.

The method writes to a redis client:

redis_client = get_redis_client()
redis_client.set('temp-facility-data', cPickle.dumps(df))

Later in the assert the result is retrieved:

res = cPickle.loads(get_redis_client().get('temp-facility-data'))
expected = pd.Series([set([1, 2, 3, 4, 5])], index=[1])
assert_series_equal(res.variation_pks, expected)

I managed to patch the redis client's get() and set() successfully.

@mock.patch('redis.StrictRedis.get')
@mock.patch('redis.StrictRedis.set')
def test_identical(self, mock_redis_set, mock_redis_get):
    mock_redis_get.return_value = ???
    f2 = deepcopy(self.f)
    f3 = deepcopy(self.f)
    f2.pk = 2
    f3.pk = 3
    self.one_row(f2, f3)

but I don't know how to set the return_value of get() to what the set() would set in the code, so that the test would pass.

Right now this line fails the test:

res = cPickle.loads(get_redis_client().get('temp-facility-data'))
TypeError: must be string, not MagicMock

Any advice please?

Answer 1

Think you can use side effect to set and get value in a local dict

data = {}
def set(key, val):
    data[key] = val

def get(key):
    return data[key]

mock_redis_set.side_effect = set
mock_redis_get.side_effect = get

not tested this but I think it should do what you want