fix: add missing dependency (pylibjuju)

[tonyandrewmeyer]

The tests use importlib.metadata to get the installed version of pylibjuju (tests/conftest.py):

    if juju_version := os.environ.get("LIBJUJU_VERSION_SPECIFIER"):
        juju_version.replace("==", "")
        juju_version = juju_version[2:].split(".")[0]
    else:
        juju_version = version("juju")

However, pylibjuju is not installed as part of the requirements. This means that all tests fail with an error like:

ERROR tests/unit/test_data_interfaces.py::TestDatabaseProvides::test_database_requested_event - importlib.metadata.PackageNotFoundError: No package metadata was found for juju

This is fixed by installing pylibjuju for the unit environment as well as integration. Alternatively, the version("juju") could be wrapped in a try/except, and you could fall back to a hard-coded version?

[shayancanonical]

TIL: tox env var substitutions. LGTM!

[deusebio]

Looks good! I would just update the reference to the juju to something more recent than 2.9.x

[tonyandrewmeyer]

Looks good! I would just update the reference to the juju to something more recent than 2.9.x

It's the same as you have for your integration tests (I assumed you'd want it to match), but happy to change it to whatever you'd prefer.

[deusebio]

We tests a number of versions, among which 2.9.42.4 which is the oldest. I would just keep on testing on CI on that one, but I would move the default reference to latest, e.g. 3.5.0.0. Otherwise the reference would already seem out of date.

I don't think that should break anything, transitive dependencies included in tox.ini are not resolved in charmlib anyway... :D