- citycountrywrite function that accepts two parametersa city name and country name the function should return single string of the form citycountrysuch as santiagochile store the function in module called city _functions py create 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 testwrite method called test_city_country(to verify that calling your function with values such as 'santiagoand 'chileresults in the correct string run test_cities pyand make sure test_city_country(passes - populationmodify your function so it requires third parameterpopulation it should now return single string of the form citycountry population xxxsuch as santiagochile population run test_cities py again make sure test_city_country(fails this time modify the function so the population parameter is optional run test_cities py againand make sure test_city_country(passes again write second test called test_city_country_population(that verifies you can call your function with the values 'santiago''chile'and 'population= run test_cities py againand make sure this new test passes testing class in the first part of this you wrote tests for single function now you'll write tests for class you'll use classes in many of your own programsso it' helpful to be able to prove that your classes work correctly if you have passing tests for class you're working onyou can be confident that improvements you make to the class won' accidentally break its current behavior variety of assert methods python provides number of assert methods in the unittest testcase class as mentioned earlierassert methods test whether condition you believe is true at specific point in your code is indeed true if the condition is true as expectedyour assumption about how that part of your program behaves is confirmedyou can be confident that no errors exist if the condition you assume is true is actually not truepython raises an exception table - describes six commonly used assert methods with these methods you can verify that returned values equal or don' equal expected valuesthat values are true or falseand that values are in or not in given