Design network integration test framework for Zebra

[teor2345]

Let's create a network integration test framework for Zebra, so we can do internal testing of consensus and sync behaviour. Some of these tests should be run during CI.

Test Goals:

• zcashd compatibility
• focus on behaviour that's hard to unit tests: network, sync, chain, consensus
• minimal viable product

Some Possible Design Ideas:

• launching tests from cargo (@dconnolly ?)
• making zcashd mine blocks really fast (< 1s per block)
  • so we can quickly test a bunch of interesting network behaviours after every commit
  • using zcashd "regtest" mode
• getting stable test results
  • this might be an ongoing task
• how do we analyse, reproduce and fix failures?

Dependencies:

• restrict zebrad (Make sure Zebra can sync from a local zcashd node #509) and zcashd to local network
• initial zebrad sync and block validation (see milestones)

Out Of Scope:

• creating random transactions
• full reproducibility

Here are some possible network designs:

• zebrad only
  • Single zebrad node
  • Two zebrad nodes
  • Multiple zebrad nodes
• zcashd miner
• One zcashd and one zebrad node
• Multiple zcashd and one zebrad node
• Multiple zcashd and multiple zebrad nodes

We might also want to have tests that load fixed state.

[teor2345]

I have turned this ticket into a design ticket, with these open design questions:

• launching tests from cargo
• making zcashd mine blocks really fast (< 1s per block)
• getting stable test results
• how do we analyse, reproduce and fix failures?

I think @dconnolly had ideas about how to launch tests from cargo.

[teor2345]

This task is related to #1004, if we decide to do it, we should just re-open one of them.