Iterate over Mock returned value

Question

I'm trying to Mock method that returns a list. After setting return_value, it still return a Mock object instead of list, so I can't iterate over that object.

Example of function that I want to test:

def func(db_engine):
    query = f"SELECT * FROM table"
    query_result = db_engine.execute(query).fetchall()
    extracted_val = []
    for res in query_result:
        extracted_val.append(res[1])
    return extracted_val

Example of test:

def test_fun():
    query = MagicMock()
    query_res = [("name_1", "value_1"), ("name_2", "value_2")]
    expected_vals = ["value_1", "value_2"]
    db_engine = MagicMock()
    db_engine.execute(query).fetchall().return_value = query_res
    vals = func(db_engine)
    assert expected_vals == vals

In summary, db_engine.execute(query).fetchall() must return list, so I can iterate over query_result, but it doesn't happens. Althou query_result has a correct values in atribute return_value, I can't iterate over it.

score 0 · Answer 1 · answered Apr 29 '20 at 05:44

You can find how to mock chained call doc here. Here is the unit test solution:

func.py:

def func(db_engine):
    query = f"SELECT * FROM table"
    query_result = db_engine.execute(query).fetchall()
    extracted_val = []
    for res in query_result:
        extracted_val.append(res[1])
    return extracted_val

test_func.py:

import unittest
from func import func
from unittest.mock import MagicMock


class TestFunc(unittest.TestCase):
    def test_func(self):
        query_res = [("name_1", "value_1"), ("name_2", "value_2")]
        expected_vals = ["value_1", "value_2"]
        db_engine = MagicMock()
        execute = db_engine.execute.return_value
        execute.fetchall.return_value = query_res
        vals = func(db_engine)

        db_engine.execute.assert_called_with("SELECT * FROM table")
        execute.fetchall.assert_called_once()
        self.assertEqual(expected_vals, vals)


if __name__ == '__main__':
    unittest.main()

unit test results with 100% coverage:

.
----------------------------------------------------------------------
Ran 1 test in 0.001s

OK
Name                                      Stmts   Miss  Cover   Missing
-----------------------------------------------------------------------
src/stackoverflow/61318070/func.py            7      0   100%
src/stackoverflow/61318070/test_func.py      16      0   100%
-----------------------------------------------------------------------
TOTAL                                        23      0   100%

Python version: Python 3.7.5

Iterate over Mock returned value

1 Answers1