[Python] How to patch a click cli app for unit testing

I have a cli tool written in Python using Click:

cli/main.py

import click
from datetime import *
from .utils import fn

@click.group(invoke_without_command=True, context_settings = { 'ignore_unknown_options': True, 'allow_extra_args': True })
@click.argument('args', nargs=-1)
def cli(args):
print(fn())

if __name__ == "__main__":
cli([])


cli/utils.py

def fn():
return("Example")


tests/test.py

from click.testing import CliRunner
from mock import *

from cli.main import cli

@patch('cli.utils.fn')
class Test:
def test_patch_fn(self, mock_fn: Mock):

mock_fn.return_value = "Mocked return"

runner = CliRunner()
result = runner.invoke(cli, [])

assert result.exit_code == 0
assert result.stdout == "Mocked return"


Running the test gives:

FAILED tests/test.py::Test::test_patch_fn - AssertionError: assert 'Example\n' == 'Mocked return'


ok, so the patching failed. I tried the following with varying results:

patch string error
cli.main.cli.utils.fn ModuleNotFoundError: No module named 'cli.main.cli'; 'cli.main' is not a package
tests.test.cli.fn AttributeError: <Group cli> does not have the attribute 'fn'
cli.fn AttributeError: <module 'cli' from '/home/user/code/click-example/cli/__init__.py'> does not have the attribute 'fn'
cli.main.cli.fn AttributeError: <Group cli> does not have the attribute 'fn'

What is the magic string I need to make this work?

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