book: add section about private testnet testing

[conradoplg]

Motivation

We want to document how to do a private testnet testing, so that we can more easily make another one in the future when required.

Specifications & References

Solution

Tests

Follow-up Work

PR Author's Checklist

• The PR name will make sense to users.
• The PR provides a CHANGELOG summary.
• The solution is tested.
• The documentation is up to date.
• The PR has a priority label.

PR Reviewer's Checklist

• The PR Author's checklist is complete.
• The PR resolves the issue.

[mpguerra]

some minor typo fixes

[arya2]

Thank you for the documentation!

There aren't any blockers, I left a few minor suggestions but they can all be safely ignored.

[arya2]

Optional/Nitpick:

Suggested change

	The objective of a private testnet test is to test testnet activation in an
	isolated fashion, before the actual testnet activation. It is usually
	done using the current state of the existing testnet. For NU6, it was done
	The objective of a private Testnet test is to test Testnet activation of an upcoming
	network upgrade in an isolated fashion, before the actual Testnet activation.
	It is usually done using the current state of the existing Testnet. For NU6, it was done

[arya2]

Optional/Nitpick:

Suggested change

	Make a backup of your current testnet state. Rename/copy the `testnet` folder to
	`unknowntest` (because that is the name used by Zebra for custom testnets).
	Make a backup of your current Testnet state. Rename/copy the `testnet` folder in
	Zebra's state cache directory to the lowercase version of the configured network name,
	or the default `unknowntestnet` if no network name is explicitly configured.

[arya2]

Great point!

Optional/Nitpick:

Suggested change

	have a (testnet) wallet connected to your lightwalletd server.
	have a (Testnet) wallet connected to your lightwalletd server.

[arya2]

I recall us using ~30-40 blocks too, it might be better to suggest a range and note that we can usually speed up mining on Testnet or stall it altogether if we're using a different network magic.

It might also be easier to test Zebra's behaviour at the network upgrade activation under varying conditions by by restarting it to drop non-finalized blocks if it's a little further from Zebra's finalized tip.

[arya2]

This is a good note, I think we forgot to do this in our first attempt and had to set a new activation height. We may want to offer creating a new branch as an example of how to modify Zebra's relevant dependencies, though it does seem like the best way (alternatives could be to use a path or make modifications in the local Cargo registry then use cargo build --offline).

Optional/Nitpick:

Suggested change

	While Zebra allows creating a private testnet in the config file, the height is
	While Zebra allows creating a private Testnet in the config file, the height is

[arya2]

This is issue #7893, it seems to affect the cached peer list as well, though it may be desirable to avoid caching inbound connection addresses in that case.

[arya2]

Suggested change

	# if you want to enable mining
	# if you want to enable mining, which also requires selecting the `internal-miner` compilation feature