How to test a function that is using user-interface - python-3.x

Question

I am trying to test a function that needs an interaction of the user. The question is how can I do it programmatically ?
Here is an example where we ask for the user to select an item in a list (main.py) :
import tkinter as tk
from tkinter import Button, OptionMenu, StringVar
def ask_for_item_in_list(lst, title, default_index=0):
root, item = tk.Tk(), None
WIDTH, HEIGHT = 300, 120
root.title(title)
root.maxsize(width=WIDTH, height=HEIGHT)
root.minsize(width=WIDTH, height=HEIGHT)
root.resizable(0, 0)
variable = StringVar(root)
variable.set(lst[default_index])
option_menu = OptionMenu(root, variable, *lst)
option_menu.pack(fill="none", expand=True)
def on_close():
# The window has been closed by the user
variable.set(None)
close()
def close():
# It quits mainloop()
root.quit()
# It closes the window
root.destroy()
button_ok = Button(root, text='OK', command=close)
button_ok.pack(fill='none', expand=True)
root.protocol('WM_DELETE_WINDOW', on_close)
# Execution stops here as long as the user has not closed the window or
# pressed ok
root.mainloop()
# We retrieve the selected item
item = variable.get()
if item == 'None':
item = None
return item
if __name__ == '__main__':
lst = ['Item 1', 'Item 2', 'Item 3']
title = 'Select an item'
default_selected_idx = lst.index('Item 2')
selected_item = ask_for_item_in_list(lst, title, default_selected_idx)
print(selected_item)
I used pytest to write all my tests since I can't use object oriented programming. Actually, the code must be maintainable by people who are not professional developpers.
As you can see, I can't test this function this way, since it will wait for the user input (test_main.py):
from main import ask_for_item_in_list
def test_ask_for_item_in_list():
lst = ['Item 1', 'Item 2', 'Item 3']
title = 'Select an item'
# Here TRY to test if changing the default selected index works
default_selected_idx = lst.index('Item 2')
# Code to simualte that the user as clicked on OK ?
# user.click_button('OK') ?
selected_item = ask_for_item_in_list(lst, title, default_selected_idx)
assert selected_item == 'Item 2'
Do I need to change the way I have coded this ?
Is it relevant to test this kind of function ?
I have faced this problem many times (whatever is the language used), I would like to know how this is supposed to be done in a clean way.
Thanks for reading ! :)

Answer 1

Usually one fills the user input beforehand with expected or special values and then calls the test function several times. Also you may simulate clicks with various tools.
In C++ you could do something like:
int number_of_tests = 10;
int tests_passed = 0;
tests_passed += my_test_function_int(0);
tests_passed += my_test_function_int(-1);
...
tests_passed += my_test_function_string("foo");
tests_passed += my_test_function_string("");
tests_passed += my_test_function_string(" ");
...
return (tests_passed == number_of_tests);
This is just an example how one can do it (in our company we do it this way).
Also it is not very hard to add new tests for non-programmers or new people.