I looked around a bit on SO but didn't find what I am looking for, I am pretty sure this has been answered elsewhere. So I have two file writes in my function like this:
def write_files():
with open("a.txt", 'w') as f_h:
f_h.write("data1")
with open("b.txt", 'w') as f_h:
f_h.write("data2")
How do I mock the f_h.write() selectively so that one returns an exception and the other does not? I tried to set side_effect but its not clear where that fits. The test code that I have experimented with has something like this:
from unittest.mock import patch, call, mock_open
import unittest
class Tester(unittest.TestCase):
def test_analyze(self):
with patch("builtins.open", mock_open(read_data="data")) as mf:
# mf.side_effect = [None, Exception()] ?
write_files()
if __name__ == '__main__':
unittest.main()
Two things: you have to mock the context manager, e.g. the result of __enter__
, and you have to put the side effect on the write
method of the mocked file handle (e.g. the result of the __enter__
call):
class Tester(unittest.TestCase):
def test_analyze(self):
with patch("builtins.open", mock_open(read_data="data")) as mf:
fh_mock = mf.return_value.__enter__.return_value
fh_mock.write.side_effect = [None, Exception]
with self.assertRaises(Exception):
write_files()