How much do you cover your code with tests? How do you write tests?

I strive to cover code with tests as comprehensively as possible, especially critical and complex parts. I usually write unit tests using the standard modules unittest or pytest.

Approach to writing tests:

• Tests should be isolated and independent.
• I use fixtures and mock objects to simulate external dependencies.
• I check both positive and negative scenarios.
• I write tests in parallel with feature development (TDD, if possible).

Example of a simple test with pytest:

import pytest

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


def test_add():
    assert add(2, 3) == 5
    assert add(-1, 1) == 0