added unit test for demo function

def an_arbitrary_functions(*args):

    """ an arbitrary function """

    print("Hi, this is an arbitrary function.")

    for _ in args:

        print(_)

def a_demo_function(*args):

    """ a demo function """

    return None

from .flip_image import flip_image, read_test_image

from .some_other_modules import an_arbitrary_functions

from .some_other_modules import a_demo_function

__all__ = ["flip_image", "read_test_image", "an_arbitrary_functions"]

__all__ = ["flip_image", "read_test_image", "a_demo_function"]

import unittest

from csst_proto.top_level_interface import a_demo_function

class TestCaseDemoFunction(unittest.TestCase):

    def test_demo_function(self):

        # flip test image

        self.assertTrue(

            a_demo_function(1) is None

        )