make all fixtures to be function scoped

[skshetry]

We should provide function scoped by default for correctness, and we can offer fixtures with a different scope if needed.

Ideally, it'd look something like this:

def s3_server_impl():
   yield MockedS3Server()

@pytest.fixture():
def s3_server():
   yield s3_server_impl()

@pytest.fixture(scope="session"):
def session_s3_server():
   yield s3_server_impl()

...

[shcheklein]

I hit an issue in trying to use pytest-servers in Studio tests. My 2cs (from a very brief interaction and research) - it's fine that server is running once per session to my mind (it takes at least a few seconds to launch it). But what hit me is that we are modifying environment variables (to pass secrets, etc) - that can conflict with some existing tests that are using regular S3 or minio or something else.

Can we start by isolating that first? Can we wrap credentials as a separate function scoped fixture that clients could use if it's needed.

WDYT, folks?

@skshetry could give more motivation behind making the server function scoped?

Also, pytest supports dynamic scopes - we might take a look into it.

[dtrifiro]

Hey @shcheklein

In #137 I got rid of the session-scoped s3_fake_creds_file while keeping the s3 server session-scoped. This should make configuration of the fixture easier, as well avoiding patching env vars.