I have a CLI tool, and would like to test that the user is prompted to confirm a choice using input()
. This would be equivalent as using raw_input()
in Python 2.
The (paraphrased) code to test looks like:
import sys
import argparse
def confirm():
notification_str = "Please respond with 'y' or 'n'"
while True:
choice = input("Confirm [Y/n]?").lower()
if choice in 'yes' or not choice:
return True
if choice in 'no':
return False
print(notification_str)
def parse_args(args):
parser = argparse.ArgumentParser()
parser.add_argument('-d', '--destructive', action='store_true')
return parser.parse_args()
def main():
args = parse_args(sys.argv[1:])
if args.destructive:
if not confirm():
sys.exit()
do_stuff(args)
if __name__ == '__main__':
main()
I am using pytest as my framework. How do I make it so I can test that the confirmation prompt is showing up in the CLI? If I try to compare stdout
I get the error: OSError: reading from stdin while output is captured
.
I want to make sure that:
I will be using the following code in another file:
import pytest
from module_name import main
def test_user_is_prompted_when_destructive_flag_is_set():
sys.argv['', '-d']
main()
assert _ # What the hell goes here?
def test_user_is_not_prompted_when_destructive_flag_not_set():
sys.argv['',]
main()
assert _ # And here too?
Optional Arguments To add an optional argument, simply omit the required parameter in add_argument() . args = parser. parse_args()if args.
You can pass arguments to fixtures with the params keyword argument in the fixture decorator, and you can also pass arguments to tests with the @pytest. mark. parametrize decorator for individual tests.
import pytest from argparse import ArgumentParser, _StoreAction ap = ArgumentParser(prog="cli") ap. add_argument("cmd", choices=("spam", "ham")) ap. add_argument("-a", "--arg", type=str, nargs="?", default=None, const=None) ...
I would suggest that starting testing with the confirm()
function is a better unit test strategy. This allows things like input
and sys.stdio
to be mocked more locally. Then once assured confirms works as expected, tests can be written that verify that it is called in specific ways. You can write tests for that, and mock confirm()
during those tests.
Here is a unit test forconfirm()
that uses pytest.parametrize
and mock
to deal with user input and output:
@pytest.mark.parametrize("from_user, response, output", [
(['x', 'x', 'No'], False, "Please respond with 'y' or 'n'\n" * 2),
('y', True, ''),
('n', False, ''),
(['x', 'y'], True, "Please respond with 'y' or 'n'\n"),
])
def test_get_from_user(from_user, response, output):
from_user = list(from_user) if isinstance(from_user, list) else [from_user]
with mock.patch.object(builtins, 'input', lambda x: from_user.pop(0)):
with mock.patch('sys.stdout', new_callable=StringIO):
assert response == confirm()
assert output == sys.stdout.getvalue()
pytest.mark.parametrize
allows a test function to be easily called multple times with conditions. Here are 4 simple steps which will test most of the functionality in confirm
:
@pytest.mark.parametrize("from_user, response, output", [
(['x', 'x', 'No'], False, "Please respond with 'y' or 'n'\n" * 2),
('y', True, ''),
('n', False, ''),
(['x', 'y'], True, "Please respond with 'y' or 'n'\n"),
])
mock.patch
can be used to temporarily replace a function in module (among other uses). In this case it is used to replace input
and sys.stdout
to allow inject user input, and capture printed strings
with mock.patch.object(builtins, 'input', lambda x: from_user.pop(0)):
with mock.patch('sys.stdout', new_callable=StringIO):
finally the function under test is run and the output of the function and any string printed are verified:
assert response == confirm()
assert output == sys.stdout.getvalue()
import sys
from io import StringIO
import pytest
from unittest import mock
import builtins
def confirm():
notification_str = "Please respond with 'y' or 'n'"
while True:
choice = input("Confirm [Y/n]?").lower()
if choice in 'yes' or not choice:
return True
if choice in 'no':
return False
print(notification_str)
@pytest.mark.parametrize("from_user, response, output", [
(['x', 'x', 'No'], False, "Please respond with 'y' or 'n'\n" * 2),
('y', True, ''),
('n', False, ''),
(['x', 'y'], True, "Please respond with 'y' or 'n'\n"),
])
def test_get_from_user(from_user, response, output):
from_user = list(from_user) if isinstance(from_user, list) \
else [from_user]
with mock.patch.object(builtins, 'input', lambda x: from_user.pop(0)):
with mock.patch('sys.stdout', new_callable=StringIO):
assert response == confirm()
assert output == sys.stdout.getvalue()
pytest.main('-x test.py'.split())
============================= test session starts =============================
platform win32 -- Python 3.6.3, pytest-3.3.2, py-1.5.2, pluggy-0.6.0
rootdir: C:\Users\stephen\Documents\src\testcode, inifile:
collected 4 items
test.py .... [100%]
========================== 4 passed in 0.15 seconds ===========================
confirm()
:To test that confirm is called when expected, and that the program responds as expected when called, you can use unittest.mock
to mock confirm()
.
Note: In the usual unittest scenario, confirm
would be in a different file and mock.patch
could be used in a similiar manner to how sys.argv
is patched in this example.
confirm()
:import sys
import argparse
def confirm():
pass
def parse_args(args):
parser = argparse.ArgumentParser()
parser.add_argument('-d', '--destructive', action='store_true')
return parser.parse_args()
def main():
args = parse_args(sys.argv[1:])
if args.destructive:
if not confirm():
sys.exit()
import pytest
from unittest import mock
@pytest.mark.parametrize("argv, called, response", [
([], False, None),
(['-d'], True, False),
(['-d'], True, True),
])
def test_get_from_user(argv, called, response):
global confirm
original_confirm = confirm
confirm = mock.Mock(return_value=response)
with mock.patch('sys.argv', [''] + argv):
if called and not response:
with pytest.raises(SystemExit):
main()
else:
main()
assert confirm.called == called
confirm = original_confirm
pytest.main('-x test.py'.split())
============================= test session starts =============================
platform win32 -- Python 3.6.3, pytest-3.3.2, py-1.5.2, pluggy-0.6.0
rootdir: C:\Users\stephen\Documents\src\testcode, inifile:
collected 3 items
test.py ... [100%]
========================== 3 passed in 3.26 seconds ===========================
enter code here
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