Dpos.getRoundDelegates returns outdated list

[lsilvs]

Expected behavior

I expect to get the correct list of delegates when calling Dpos.getRoundDelegates after a new round is reverted and previous round changes the delegate list.

Actual behavior

It always uses the cached list ignoring possible changes on the list when a block is reverted.

Steps to reproduce

1. Call Dpos.getRoundDelegates(R2) where R2 is the beginning of a new round
2. Revert the last blocks so that we return to the previous round (R1)
3. Unvote an active delegate and vote for a new one during the previous round (R1)
4. Call Dpos.getRoundDelegates(R2) again in the beginning of the next round (R2)

Because Dpos.getRoundDelegates caches every new list and never clears it, it returns an outdated list ignoring the changes made after the last block of the round is reverted.

Step 4 should return a new delegate list including the new voted delegate and excluding the unvoted delegate.

Which version(s) does this affect? (Environment, OS, etc...)

feature/introduce_bft_consensus

[lsilvs]

Please, unskip these test as part this issue: https://github.com/LiskHQ/lisk-sdk/pull/4154/commits/b185320b3e1f5ac5a90057175db43b0b7d9ba319

[yatki]

@lsilvs seems like processor is not using dpos.undo for deleting the block. That's why those 2 tests are still failing. @shuse2 should I create an issue for unskipping these tests when undo is implemented?

[shuse2]

I think we can add back those 2 test on dpos.undo issue