python - Getting started with unit testing for functions without return values -

i've got program that's built on functions taks user inputs inside functions , not parameters before function: example, function

def my_function():     = input("a: ")     b = input("b: ")     print(a+b) 

and understand far unit testing function harder unit test function works example this:

def another_function(a,b):     return(a+b) 

so how go testing function looks my_function, example? feels if easy test manually entering incorrect inputs , checking errors, have write test suite tests functions automatically.

given function input comes input , output goes print, have "mock" both of these functions test my_function. example, using simple manual mocking:

def my_function(input=input, print=print):     = input("a: ")     b = input("b: ")     print(a+b)  if __name__ == '__main__':     inputs = ['hello', 'world']     printed = []      def mock_input(prompt):         return inputs.pop(0)      def mock_print(text):         printed.append(text)      my_function(mock_input, mock_print)     assert len(inputs) == 0, 'not input used'     assert len(printed) == 1, '{} items printed'.format(len(printed))     assert printed[0] == 'helloworld' 

when compare to:

assert my_function('hello', 'world') == 'helloworld' 

you can see why latter preferred!

you use proper mocking library more neatly, without having supply functions arguments; see e.g. how supply stdin, files , environment variable inputs python unit tests?.