Add zebra_state::init_test helper function for tests

[jvff]

Motivation

As part of the work for #1334, the construction of a state service instance will change a bit, because it will return a view to the current best chain tip block height. This will require changes to all tests that create a state service. To streamline these changes and to simplify the test code, this PR introduces an alternative constructor for tests to use.

Solution

The zebra_state::init_test function is available to other crates when the proptest-impl feature is enabled. The function creates a state service with an ephemeral Config and automatically wraps the service in a Buffer with one slot. These are the most common defaults for the tests, so it reduces a little the amount of repeated code.

Review

@teor2345 is reviewing the set of changes that are part of #1334.

Reviewer Checklist

• Code implements Specs and Designs
• Tests for Expected Behaviour
• Tests for Errors

Follow Up Work

A follow-up PR will actually change the zebra_state::init method, but after this PR most tests will not need any extra changes.

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This change is 

[teor2345]

It seems like there are some changes missing from the commits in this PR?

[teor2345]

Reviewed 6 of 6 files at r1.
Reviewable status: all files reviewed, 2 unresolved discussions (waiting on @jvff)

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zebra-state/src/service.rs, line 753 at r1 (raw file):
Can we document the ephemeral config and buffer size here?

The buffer size doesn't really matter, because the underlying service is always ready, and there won't be much contention in the tests. So it just needs to be documented.

/// Initialize a state service with an ephemeral [`Config`].
///
/// This can be used to create a state service for testing. See also [`init`].

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zebra-state/src/service.rs, line 754 at r1 (raw file):

///
/// This can be used to create a state service for testing. See also [`init`].
#[cfg(any(test, feature = "proptest-impl"))]

Do some of the dependent crates need to activate zebra-chain's proptest-impl feature so they can see this function?

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zebra-state/src/service/tests.rs, line 24 at r1 (raw file):

        .map(|block| Request::CommitFinalizedBlock(block.into()));

    let network = Network::Mainnet;

Adding buffers to these tests shouldn't change test behaviour.
But let's make sure CI passes before we merge.

[jvff]

Oops, yeah. Fixed now 😄

Reviewable status: 5 of 7 files reviewed, 2 unresolved discussions (waiting on @jvff and @teor2345)

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zebra-state/src/service.rs, line 753 at r1 (raw file):

Previously, teor2345 (teor) wrote…

Can we document the ephemeral config and buffer size here?

The buffer size doesn't really matter, because the underlying service is always ready, and there won't be much contention in the tests. So it just needs to be documented.

/// Initialize a state service with an ephemeral [`Config`].
///
/// This can be used to create a state service for testing. See also [`init`].

Done.

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zebra-state/src/service.rs, line 754 at r1 (raw file):

Previously, teor2345 (teor) wrote…

Do some of the dependent crates need to activate zebra-chain's proptest-impl feature so they can see this function?

Done.

[teor2345]

Reviewed 2 of 2 files at r2.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @jvff)