[Tests] Add mempool_limit.py test

[jonasschnelli]

This will test mempools tx eviction (-maxmempool) together with the new conflict handling (#7105)

[maflcko]

If you copied this code, DRY?

[jonasschnelli]

Yes. I think this code part is in maxuploadtarget.py, prioritise_transaction.py and pruning.py. Someone should refactor that once. I have original taken this from a test that @sdaftuar wrote.

[maflcko]

Mind to do it in this PR like 826079e?

[maflcko]

It's enough to review this method once and not every time a pull tester PR is opened.

[jonasschnelli]

Nits addresses: refactored the shared functions (moved to util.py).

[maflcko]

Can you do the same here?

    def __init__(self):
        self.txouts = create_many_txouts()

[jonasschnelli]

This part needs to be refactored between 4 existing tests.
This PRs intent is not to refactor the test framework instead it should add a mempool limit/eviction test.

[maflcko]

Consider it a NIT but I don't like having the same code in 4 locations. You are guaranteed to get a bug out of that some day. (We already had it with other rpc tests)

[laanwj]

Having the same code in 4 locations only makes sense if it is expected to diverge again later. Over-eager de-duplication can result in more complex code in such cases.

I don't think that's the case here. But I also agree with @jonasschnelli that refactoring is not required in a PR that adds a test.

[maflcko]

utACK 7632cf6. Runs for 4 secs, so should be ok to run every time.

[laanwj]

utACK jonasschnelli@7632cf6