py.test patch on fixture

I’d say patching via decorator is not the optimal approach here. I’d use the context manager:

import pytest
from unittest.mock import patch


@pytest.fixture(autouse=True)
def no_delay():
    with patch('ConstantsModule.ConstantsClass.DELAY_TIME', 10):
        yield

This way, patching is cleanly reverted on test teardown.