Decorator for registering a function with key. It was wrong (until version 3), but now it works, thanks Real Python and Kryssz90

loader_factory.py

import functools
import unittest
from typing import Callable


class LoaderFactory:

    def __init__(self) -> None:
        self.registered_functions = dict(
        )

    def get_loader_function(self, registeredName: str) -> Callable:
        return self.registered_functions.get(registeredName, default_function)

    def register_loader_function(self, registeredName: str, function: Callable) -> None:
        self.registered_functions[registeredName] = function


private_property_factory = LoaderFactory()


def default_function(x):
    return 3*x


def register(registeredName):
    """Registers the loader function"""

    def decorator_register(func):
        private_property_factory.register_loader_function(registeredName, func)

        @functools.wraps(func)
        def wrapper(*args, **kwargs):
            print(3, private_property_factory.registered_functions)
            value = func(*args, **kwargs)
            return value
        return wrapper
    print(2, private_property_factory.registered_functions)
    return decorator_register


@register('StartProcess')
def function1(x):
    return 2*x


print(1, private_property_factory.registered_functions)

print(4, private_property_factory.get_loader_function("StartProcess")(15))  # Doesn't print the registered functions, function1 was registered without the wrapper.
print(5, function1(15))  # It prints the registered functions, as we call the wrapped function.


class MyTestCase(unittest.TestCase):
    def test_something(self):
        self.assertIn('StartProcess', private_property_factory.registered_functions)


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

It's worth to try what will be the output of this script.
There is five print statements starting with print(1,..., print(2,... ... print(5, ...). What will be the order of this prints.