feat: Allow running subsets of test cases

[phoevos]

• Allow running only a subset of the provided tests using pytest's filtering feature with the -k command-line option, which facilitates (de)selecting the test cases to run filtering on their name
• Introduce a dedicated tox testenv for running all tests apart from the ones that assume MLFlow integration
• Update README with instructions on using the newly added functionality

Closes #6

[i-chvets]

Checked out branch and tried to run some tests according to instructions. Tests failed:

$ pytest -k "kfp"
platform linux -- Python 3.10.12, pytest-7.4.0, pluggy-1.2.0 -- /home/ichvets/charmed-kubeflow-uats/venv/bin/python3
cachedir: .pytest_cache
rootdir: /home/ichvets/charmed-kubeflow-uats/tests
configfile: pytest.ini
collected 5 items / 4 deselected / 1 selected                                                                     

test_notebooks.py::test_notebook[kfp-integration] 
-------------------------------------------------- live log call --------------------------------------------------
INFO     test_notebooks:test_notebooks.py:37 Running kfp-integration.ipynb...
WARNING  traitlets:kernelspec.py:286 Kernelspec name python3 cannot be found!
ERROR    traitlets:manager.py:92 No such kernel named python3
Traceback (most recent call last):
  File "/home/ichvets/charmed-kubeflow-uats/venv/lib/python3.10/site-packages/jupyter_client/manager.py", line 85, in wrapper
    out = await method(self, *args, **kwargs)
  File "/home/ichvets/charmed-kubeflow-uats/venv/lib/python3.10/site-packages/jupyter_client/manager.py", line 397, in _async_start_kernel
    kernel_cmd, kw = await self._async_pre_start_kernel(**kw)
  File "/home/ichvets/charmed-kubeflow-uats/venv/lib/python3.10/site-packages/jupyter_client/manager.py", line 359, in _async_pre_start_kernel
    self.kernel_spec,
  File "/home/ichvets/charmed-kubeflow-uats/venv/lib/python3.10/site-packages/jupyter_client/manager.py", line 182, in kernel_spec
    self._kernel_spec = self.kernel_spec_manager.get_kernel_spec(self.kernel_name)
  File "/home/ichvets/charmed-kubeflow-uats/venv/lib/python3.10/site-packages/jupyter_client/kernelspec.py", line 287, in get_kernel_spec
    raise NoSuchKernel(kernel_name)
jupyter_client.kernelspec.NoSuchKernel: No such kernel named python3
FAILED                                                                                                      [100%]

[i-chvets]

The functionality that this PR introduces works correctly, i.e. proper tests are selected when -k option is used.

[phoevos]

@i-chvets, I have seen this error before and it's due to running the test inside a virtual environment. That won't work out of the box, you'd have to set up some Jupyter/ipython related stuff, hence it's not in the instructions.

This is supposed to be executed from inside a notebook where you'd usually just pip install the requirements user-wide (That's what the driver automation does ATM anyway).

[i-chvets]

@i-chvets, I have seen this error before and it's due to running the test inside a virtual environment. That won't work out of the box, you'd have to set up some Jupyter/ipython related stuff, hence it's not in the instructions.

This is supposed to be executed from inside a notebook where you'd usually just pip install the requirements user-wide (That's what the driver automation does ATM anyway).

Understood. Approving.

[i-chvets]

Approved. ACK tests should not be executed in virtual env, but in the notebook.