What is unit testing?

Unit testing is the process of testing individual, smallest isolated logical blocks of code (modules, functions, methods) in an application.

Main goals of unit testing:

• Verification of the correctness of each module in isolation.
• Early detection of defects at the code level.
• Facilitation of refactoring and code maintenance.
• Providing documentation on module operation.

Characteristics of unit testing:

• Performed by developers.
• Focused on checking the business logic of the module, not on interaction with external dependencies (databases, file systems, networks).
• Uses test frameworks (JUnit, NUnit, Pytest, Mocha, etc.).
• Often employs stubs, mocks, or fixtures to isolate the tested module.

Example of a Python unit test using Pytest:

# test_math_functions.py

import pytest
from math_functions import add, subtract

def test_add_positive_numbers():
    # Testing addition of positive numbers
    assert add(2, 3) == 5

def test_add_negative_numbers():
    # Testing addition of negative numbers
    assert add(-1, -4) == -5

def test_subtract_positive_numbers():
    # Testing subtraction of positive numbers
    assert subtract(5, 2) == 3

def test_subtract_with_negative_result():
    # Testing subtraction with a negative result
    assert subtract(2, 5) == -3