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:

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