Cannot test a container entrypoint easily

[dcermak]

pytest_container can be used to test containers that run a persistent service, but it is rather inconvenient to test one-shot-style containers which only exist to run their CMD/ENTRYPOINT. For such a container image, you generally just want to invoke it as podman run --rm -it $img $params and act on the output/side effects.

At the moment, pytest_container provides no convenient way how to achieve this. One potential possible way is to use testinfra directly:

SOME_CTR = Container( ... )

def test_some_ctr(host, container_runtime):
    out = host.check_output(f"{container_runtime.runner_binary} run --rm -it {SOME_CTR.url}")
    # do smth with out

However, that quickly breaks down, when SOME_CTR is no longer a Container but a DerivedContainer as then we need to build the container beforehand. Executing this manually is laborious and inconvenient. It would be great to provide a helper or a new fixture here.