What could be a pytest file for this program?

Question

I have written this program as my final project. How would I write a pytest file to assure the program is properly tested. It really confused me since the functions I implemented in the program do NOT return values when executed. Please give an example of get_user_input() function and how can I pytest assure it.

import sys

def main():
    print("~~~~~~~~~~~~~~~~~~~~~~~~~ Welcome to the Expense Tracker ~~~~~~~~~~~~~~~~~~~~~~~~~")
    print("This program helps track your total expenses according to their categories")
    print("Please Note that the categories are Utilities, Rent, Insurance, Entertainment, Travel & Payroll")
    categories = ["utilities", "rent", "insurance", "entertainment", "travel", "payroll"]
    expenses = {category: [] for category in categories} #Initilizes a dictionary with empty key values (to be appended later by the function add_expense())
    
    
    while True:
        question = input("Type 1 to add one more or 2 to Quit the program to see the result: ").strip()
        if question == "1":
            get_user_input(categories, expenses)
        elif question == "2":
            view_expenses(expenses)
            sys.exit("System Quitted")  # Exit the program
        else:
            print("Invalid Input, Please type 1 to Continue or 2 to Quit")

def add_expense(amount, category, expenses):
    expenses[category].append(float(amount))  # Append the expense amount to the category list
    print("Expense added successfully!")

def view_expenses(expenses):
    print("\nCurrent Expenses:")
    total_expenses = 0
    for category, items in expenses.items():
        total_category = sum(items)
        total_expenses += total_category
        print(f"{category.capitalize()}: ${total_category:.2f}")
    print(f"\nTotal Expenses: ${total_expenses:.2f}")

def get_user_input(categories, expenses):
    while True:
        user_input = input("Please enter the amount in USD (WITHOUT DOLLAR SIGN) and the category of the expense separated by a comma: ").replace(" ", "").lower()

        if "," not in user_input:
            print("Invalid input format. Please use the format: amount, category")
            continue

        amount, category = user_input.split(",")

        if category not in categories:
            print("Invalid Category!")
            continue 
    
        else:
            add_expense(amount, category, expenses)
            break

if __name__ == "__main__":
    main()

Another off-topic question. Can that project be considered as enough for the final project? or is it not as complicated as it is required to be? What could be some tips/advices for tuning it?

Thanks!!