consensus: add comment as to why use mocks during replay

[melekes]

Closes #4766

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[codecov-io]

Codecov Report

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@@            Coverage Diff            @@
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Impacted Files	Coverage Δ
consensus/replay.go	73.64% <ø> (ø)

[erikgrinaker]

Is it much more expensive to set up an empty mempool and memory-backed evidence pool instead, or simply pass nil?

[melekes]

Is it much more expensive to set up an empty mempool and memory-backed evidence pool instead, or simply pass nil?

nil does not satisfy the interface. memory backed evidence pool - we would have to create one. evmock is pretty much the same.

[erikgrinaker]

nil does not satisfy the interface.

nil satisfies all interfaces.

memory backed evidence pool - we would have to create one. evmock is pretty much the same.

I believe @cmwaters renamed it to emptyEvidencePool or something, which I guess is slightly better.

[melekes]

nil satisfies all interfaces.

right, I forgot it. Thanks!

[melekes]

nil does not work because we call methods on mempoo/evidence pool.

[erikgrinaker]

nil does not work because we call methods on mempoo/evidence pool.

So check if it's nil? If there's a need to run this without mempool/evidence pool, then let's just make them optional?

[melekes]

So check if it's nil? If there's a need to run this without mempool/evidence pool, then let's just make them optional?

too many if conditions?