blissdata: allow testing outside conda environment

This MR allows for optional pytest arguments

pytest --redis-module-dir=/my/module/dir \
       --redis-config-file=/my/redis/redis.conf \
       --redis-exec=/my/redis/server \   # we already had this one
       ./blissdata 

Motivation

• Allow testing without conda. For example https://gitlab.esrf.fr/bliss/blissdata/-/merge_requests/11.
• Other projects which depend on blissdata need tests with a blissdata-compliant redis server. For example https://gitlab.esrf.fr/bliss/blissoda. Re-using the fixture from blissdata helps. Of course none of those projects do conda.

Will not work with pytest --pyargs blissdata.tests

Because of https://github.com/pytest-dev/pytest/issues/1596 these arguments are currently not available when running tests with --pyargs (runs the tests of the installed package, not the source directory). For example instead of

pytest -v --pyargs blissdata.tests --redis-config-file=/etc/redis/redis.conf

you will need to do

export TEST_WD=$(python -c "from blissdata import tests;print(tests.__path__[0])")
pytest -v --redis-config-file=/etc/redis/redis.conf $TEST_WD

In the Bliss CI case (which has CONDA_PREFIX) you don't needs redis arguments so this works as expected

pytest -v --pyargs blissdata.tests

Details of MR

Since we are forced to launch our own redis server because pytest-redis does not support loadmodule, the pytest-redis dependency is overkill and the fixture factory is also awkward (arguments are needed upon import, which means finding a free port upon import). So imo we can drop pytest-redis.

I also intend to reuse the redis_db in other projects that need blissdata testing with the redis modules (e.g. blissoda). Hence I defined everything in a separate module blissdata.tests.redis_server. Usage would be

# conftest.py of blissoda for example

from blissdata.tests.redis_server import add_redis_server_options
from blissdata.tests.redis_server import redis_db  # noqa F401


def pytest_addoption(parser):
    add_redis_server_options(parser)