How to write a unit test using Pytest for the main function in Python

Question

I am new with unit testing and am confused about a lot of things. In the project I have been inherited, there is a __main__.py file, in which there is only one function:

import some_class

def func1 (some_instance) -> bool:
    #some code
    #returns true or False



some_instance = some_class()
func1 (some_instance)

Now, in another file ( tests.py ), which is in the same folder as __main__.py , I want to write a unit test to test the func1 function. I don't know how I can do that. This is all I got:

import some_class
from __main__ import func1

def test_func1():
    test_instance = some_class()
    assert func1(test_instance) is True

It doesn't work and I think the test_func1() cannot even access func1 . How can import func1 ? How can I test it? The ( from __main__ import func1 ) part looks strange.

Answer 1

Let's assume that you want to test Calculator class and it's method add

# src/calculator.py

class Calculator:
    def __init__(self, x, y):
        self.x = x
        self.y = y

    def add(self):
        return self.x + self.y

Then create a test file in the same folder as calculator.py -

# src/test_calculator.py

from src.calculator import Calculator


def test_calculator_instance():
    calculator = Calculator(2, 2)
    assert isinstance(calculator, Calculator) == True


def test_calculator_addition():
    calculator = Calculator(2, 2)
    assert calculator.add() == 4

That's it. Now you just type pytest. in your terminal and you should see something as follows -

test_calculator.py ..                [100%]
===== 2 passed in 0.01s =======

I hope this helps.