Parametrized fixture based on configuration file

[jmlemetayer]

Hi folks,

I would like to be able to test multiple embedded boards at the same time using a configuration file.

My idea was to have at the end something like that:

# config.yaml

devices:
  - name: board_one
    tty_port: /dev/ttyUSB0

  - name: board_two
    tty_port: /dev/ttyUSB1

# test_a.py
import pytest

def test_one():
    pass

@pytest.mark.not_board_one
def test_two():
    pass

To do this I have started a local plugin like this:

# conftest.py
import pytest
import yaml

config = dict()
devices = list()

def pytest_configure(config):
    # Get 'config_file' from ini or options
    read_config(config_file)

def read_config(config_files):
    global config
    global devices

    for config_file in config_files:
        with open(config_file, "r") as stream:
            config = yaml.safe_load(stream)

    for device in config.get("devices", []):
        devices.append(Device(**device))

class Device:
    def __init__(self, name, tty_port):
        self.name = name
        self.tty_port = tty_port

def get_devices():
    global devices
    return devices

@pytest.fixture(scope="session", params=get_devices(), autouse=True)
def device(request):
    return request.param

I did it like this because I would like to have my test to run on all boards. But I do not want to have the device fixture mandatory, so the tests stay quite simple.

My idea was to later add some tty_port and even serial fixtures on top of that. So that a test can request a working serial link with the board just by doing:

# conftest.py
@pytest.fixture(scope="session")
def tty_port(device):
    return device.tty_port

@pytest.fixture(scope="session")
def serial(tty_port):
    # Open and configure a serial link using the tty_port
    return serial

# test_b.py

def test_three(serial):
    # Do some serial communications

But this is not working... I have an error like this:

test_a.py::test_one[device0] SKIPPED (got empty parameter set ['device'], ...)

Clearly the devices list is still empty when the fixture is constructed.

Is it possible to do something like that ? What will be the correct way to do it ? Parsing the yaml in the get_devices function is working, but I lose all the getini and getoption mechanism (not shown in the example).

Thanks in advance.