In what situations and at what moment do fixtures execute during testing?

Fixtures in testing are preparatory actions that create the necessary state for executing a test. They are performed before the test runs to ensure a stable and predictable environment. For example, a fixture might create test data, configure the environment, or initialize objects.

In most testing frameworks, fixtures are executed in methods with annotations like @Before or setup(), which are run before each test or before a set of tests. After the test, cleanup methods (e.g., @After) are often executed to restore the system to its original state.

Example in Python using pytest:

import pytest

@pytest.fixture
def setup_data():
    data = {'user': 'test', 'password': '1234'}
    return data

def test_login(setup_data):
    assert setup_data['user'] == 'test'

Here, the fixture setup_data creates data that is used in the test.