Introduce tox for testing

[giuliatum]

Closes #177

[BenjaminRodenberg]

We also have to revert this before merging but ok during development to avoid having to install preCICE on the system.

[BenjaminRodenberg]

I think there is a minor thing left. But besides that everything works very well and is a super useful (and extremely overdue) update for this repository. Thank you very much :)

Where I'm still struggling:

If I run the following command:

tox -e unit -- tests/test_write_read.py::TestWriteandReadData::test_vector_write

I get the following output:

unit: commands[0]> pytest tests/unit
==================================================================================================================== test session starts =====================================================================================================================
platform linux -- Python 3.12.3, pytest-8.3.5, pluggy-1.5.0
cachedir: .tox/unit/.pytest_cache
rootdir: /home/benjamin/Programming/fenics-adapter
configfile: pyproject.toml
collected 5 items                                                                                                                                                                                                                                            

tests/unit/test_adapter_core.py ..                                                                                                                                                                                                                     [ 40%]
tests/unit/test_checkpointing.py ...                                                                                                                                                                                                                   [100%]

====================================================================================================================== warnings summary ======================================================================================================================
../../../../usr/lib/python3/dist-packages/dijitso/__init__.py:19
  /usr/lib/python3/dist-packages/dijitso/__init__.py:19: DeprecationWarning: pkg_resources is deprecated as an API. See https://setuptools.pypa.io/en/latest/pkg_resources.html
    from pkg_resources import get_distribution

../../../../usr/lib/python3/dist-packages/pkg_resources/__init__.py:2871
  /usr/lib/python3/dist-packages/pkg_resources/__init__.py:2871: DeprecationWarning: Deprecated call to `pkg_resources.declare_namespace('mpl_toolkits')`.
  Implementing implicit namespace packages (as specified in PEP 420) is preferred to `pkg_resources.declare_namespace`. See https://setuptools.pypa.io/en/latest/references/keywords.html#keyword-namespace-packages
    declare_namespace(pkg)

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
=============================================================================================================== 5 passed, 2 warnings in 5.09s ================================================================================================================
  unit: OK (5.75=setup[0.07]+cmd[5.68] seconds)
  congratulations :) (5.87 seconds)

This looks to my like all tests in unit are run. However, actually I would like to only see a single test being run. https://stackoverflow.com/a/49935307 gives already a hint: You need pytest {posargs} somewhere in the commands. I personally would not start duplicating this in unit and integration. Instead, it would probably make sense to have a third environment (all?) where we run all tests by default and apply the filtering only if given by the user. The command that we run from the command line would look like:

tox -e all -- tests/test_write_read.py::TestWriteandReadData::test_vector_write

[BenjaminRodenberg]

Looks great! Thank you very much and congratulations to your first contribution 🎉