How can independence and isolation of tests be ensured to prevent mutual influence during execution?

To ensure independence and isolation of tests in Python, it is important that each test does not depend on the state created by other tests. This is achieved through the following methods:

• Using fixtures (for example, in pytest) to prepare and clean up the environment before and after each test.
• Avoiding global variables and state that can change between tests.
• Using mocks and stubs to isolate external dependencies.
• Running each test in a separate context or even process (for example, with pytest-xdist).

Example using a pytest fixture:

import pytest

@pytest.fixture
def setup_data():
    data = {'count': 0}
    yield data
    # cleanup if needed


def test_increment(setup_data):
    setup_data['count'] += 1
    assert setup_data['count'] == 1


def test_reset(setup_data):
    assert setup_data['count'] == 0

Here, each test receives a fresh dictionary, which prevents one test from affecting another.