City, Country: Write a function that accepts two parameters: a city name and a
country name. The function should return a single string of the form city,
country, such as santiago, Chile. Store the function in a module called city
functions.py.
Create a file called test_cities.py that tests the function you just wrote
(remember that you need to import unittest and the function you want to test).
Write a method called test_city_country () to verify that calling your
function with values such as 'santiago' and 'chile' results in the correct
string. Run test_cities.py, and make sure test_city_country() passes.
