test: move ReplicaofRejectOnLoad test from pytest into unit tests

[BorysTheDev]

added test to check that replicaof can't run during the LOADING state

[adiholden]

The idea of pytest below checks that:

1. on server start we are in loading state
2. once we move from loading state to active as we finished loading the file the replica of command success

This unit test is very limited

[BorysTheDev]

we have a lot of tests where we start replica in active state. I don't see any reason to do the same

[romange]

I do not mind adding an additional test.

[romange]

@BorysTheDev what's the reason it takes 5 minutes? It's indeed a lot

[BorysTheDev]

@BorysTheDev what's the reason it takes 5 minutes? It's indeed a lot

I didn't check but I think because of debug populate 8000000 -> save -> load operations

[adiholden]

@BorysTheDev what's the reason it takes 5 minutes? It's indeed a lot

I didn't check but I think because of debug populate 8000000 -> save -> load operations

The debug populate is the most time consuming
We added so many keys here to gauranty the time it takes to load the data is long enough to catch the fail on loading.
Instead of populating 8m keys I believe we can feel the database in another way
f.e add sets with many elements using static seeder

[romange]

Let's maybe reduce it to 4000000 ? I do not want to optimize this too much, it's not important. This PR,
#4408 touches this test, I can make the change.

[BorysTheDev]

Let's maybe reduce it to 4000000 ? I do not want to optimize this too much, it's not important. This PR, #4408 touches this test, I can make the change.

I suggest to have 3 tests instead of this one:

1. loading state during loading (pytest) - slow
2. reject replicaof during loading state (unit test) - fast
3. success replicaof after loading file (pytest) - fast