improve our pytest framework

[romange]

Currently our pytest framework in tests/pytest is very naive. It assumes that dragongly process is already running.

1. We should introduce the fixture that assumes the binary exists under gitroot/build_dbg (if DFLY_BIN env is undefined).
   this fixture should start a dragonfly process at the beginning of pytest run and be used by multiple tests. Each test should get an empty db (after flushall).

2. We should be able to parametrize this fixture in order to run dragonfly process with different flags. Tests would define which configuration they need. For example, some tests may want to test memcache protocol and access dragonfly process with memcached_port=... defined.

[romange]

1. This is very high level, I am not very familiar with pytest but based on my little knowledge of pytest it can be done there easily.
2. Finally, I want README under tests/ that explains how to run the tests under pytest.

[shmulik-klein]

@romange If not assigned, I'll take this one.

1. Is DFLY_BIN is already used? can it be more explicit such as DRAGONFLY_HOME or DRAGONFLY_BIN?
2. In the fallback, did you mean gitroot/build-opt?

[romange]

go for it and yes

[shmulik-klein]

Breaking down this issue into subtasks, here is the current status:

• Add dragonfly_db fixture to set up and tear down a DragonflyDB process
• Flush all records between each test
• Parse tests requirements and pass as flags to the executable
• Add a README for pytest tests execution guidelines

[romange]

here is the test you could do with another configuration.
run process dragonfly --proactor_threads=1 --max_memory=2097152,

and within the test start adding string entries with blobs say of 1K, after ~2000 keys you should start getting "out of memory" error at some point and this is what the test could check. This way you will have a useful example of running different configurations of dragonfly. @shmulik-klein
btw, Dragonfly rejects writes when it goes out of memory, unlike Redis which just crashes.

[Nike682631]

@romange Is this issue available to take up?

[romange]

Yes, @Nike682631 - that would be helpful