Which testing library is preferable for use in Python: pytest or unittest?

pytest is preferred for most Python projects because it is more modern, convenient, and flexible compared to unittest. pytest allows writing tests more simply and concisely, supports powerful fixtures, parameterization, and has a rich ecosystem of plugins.

unittest is a built-in module in the standard library, similar to xUnit frameworks from other languages, but requires more boilerplate code and is less convenient for writing complex tests.

Example of a simple pytest test:

import pytest

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


def test_add():
    assert add(2, 3) == 5

In conclusion, if there are no restrictions on using external libraries, it is better to choose pytest.