How and where does py.test find fixtures

Question

Where and how does py.test look for fixtures? I have the same code in 2 files in the same folder. When I delete conftest.py, cmdopt cannot be found running test_conf.py (also in same folder. Why is sonoftest.py not searched?

# content of test_sample.py
def test_answer(cmdopt):
    if cmdopt == "type1":
        print ("first")
    elif cmdopt == "type2":
        print ("second")
    assert 0 # to see what was printed

content of conftest.py

import pytest

def pytest_addoption(parser):
    parser.addoption("--cmdopt", action="store", default="type1",
        help="my option: type1 or type2")

@pytest.fixture
def cmdopt(request):
    return request.config.getoption("--cmdopt")

content of sonoftest.py

import pytest

def pytest_addoption(parser):
    parser.addoption("--cmdopt", action="store", default="type1",
        help="my option: type1 or type2")

@pytest.fixture
def cmdopt(request):
    return request.config.getoption("--cmdopt")

The docs say

http://pytest.org/latest/fixture.html#fixture-function

1. pytest finds the test_ehlo because of the test_ prefix. The test function needs a function argument named smtp. A matching fixture function is discovered by looking for a fixture-marked function named smtp.
2. smtp() is called to create an instance.
3. test_ehlo() is called and fails in the last line of the test function.

Answer 1

py.test will import conftest.py and all Python files that match the python_files pattern, by default test_*.py. If you have a test fixture, you need to include or import it from conftest.py or from the test files that depend on it:

from sonoftest import pytest_addoption, cmdopt