tests: improve clarity vm tests

[federico-stacks]

Description

Tidy-up and correctness pass over the Clarity VM unit tests (costs.rs, analysis_costs.rs, large_contract.rs, transactions.rs) and the shared test instantiation helpers. The main functional fix addresses a latent mismatch where a test's BurnStateDB epoch and the cost contracts actually deployed in the ClarityDatabase could disagree the tests still passed, but exercised the wrong costs-N contract for the epoch under test.

This issue emerged during PR #6959 where caching for ClarityDatabase epoch was introduced, making the now "fixed" tests failing.

Applicable issues

• fixes #

Additional info (benefits, drawbacks, caveats)

Checklist

• Test coverage for new or modified code paths
• For new Clarity features or consensus changes, add property tests (see docs/property-testing.md)
• Changelog fragment(s) or "no changelog" label added (see changelog.d/README.md)
• Required documentation changes (e.g., rpc/openapi.yaml for RPC endpoints, event-dispatcher.md for new events)
• New clarity functions have corresponding PR in clarity-benchmarking repo

[coveralls]

Coverage Report for CI Build 28179718097

Coverage increased (+0.3%) to 86.047%

Details

• Coverage increased (+0.3%) from the base build.
• Patch coverage: 4 uncovered changes across 1 file (187 of 191 lines covered, 97.91%).
• 8890 coverage regressions across 130 files.

Uncovered Changes

File	Changed	Covered	%
stackslib/src/chainstate/stacks/db/mod.rs	124	120	96.77%
Total (2 files)	191	187	97.91%

Coverage Regressions

8890 previously-covered lines in 130 files lost coverage.

Top 10 Files by Coverage Loss	Lines Losing Coverage	Coverage
stackslib/src/chainstate/burn/db/sortdb.rs	505	90.19%
stackslib/src/chainstate/stacks/db/blocks.rs	502	89.93%
stackslib/src/chainstate/nakamoto/mod.rs	403	84.62%
stackslib/src/config/mod.rs	376	68.96%
stackslib/src/net/mod.rs	309	78.12%
stackslib/src/chainstate/stacks/index/storage.rs	277	82.41%
clarity/src/vm/database/clarity_db.rs	268	82.11%
stackslib/src/chainstate/stacks/miner.rs	253	83.4%
stackslib/src/chainstate/stacks/db/transactions.rs	239	97.16%
stackslib/src/net/inv/epoch2x.rs	221	79.49%

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Coverage Stats

Relevant Lines:	226549
Covered Lines:	194939
Line Coverage:	86.05%
Coverage Strength:	18801135.9 hits per line

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💛 - Coveralls

[francesco-stacks]

overall looks good, I think that we start to have a bit too many initializers for StacksChainState and maybe it would improve a bit to refactor it with the builder pattern, but I also get that this is a very niche test suite, so i don't have a strong opinion about it

[federico-stacks]

overall looks good, I think that we start to have a bit too many initializers for StacksChainState and maybe it would improve a bit to refactor it with the builder pattern, but I also get that this is a very niche test suite, so i don't have a strong opinion about it

I gave the builder idea a try: b3e9510
I kept the usage hidden behind the instantiate_chainstate* methods to reduce impact on the existent tests.

[Copilot]

Pull request overview

This PR refactors and corrects Clarity VM/unit-test harness setup to ensure the epoch under test aligns with the boot cost contracts actually deployed in the underlying Clarity database/MARF. It centralizes epoch-transition setup for Clarity VM tests and expands chainstate test instantiation helpers to optionally predeploy all costs-N contracts at genesis for tests that exercise multiple epochs.

Changes:

• Add apply_transitions_for_epoch() test helper and adopt it in VM tests to reach target epochs deterministically.
• Introduce TestChainstateBuilder and new chainstate instantiation helpers to optionally deploy all costs-N contracts at genesis (and normalize chainstate_path() for :: in test names).
• Update multiple tests to use the revised helpers and tighten assertions around expected cost-contract defaults.

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
stackslib/src/core/tests/mod.rs	Switch test chainstate setup to simplified instantiation helper.
stackslib/src/clarity_vm/tests/test_utils.rs	New shared helper to run genesis + epoch transitions for VM tests.
stackslib/src/clarity_vm/tests/mod.rs	Export the new test_utils module.
stackslib/src/clarity_vm/tests/large_contract.rs	Use the shared epoch-transition helper to ensure correct cost contracts for the epoch under test.
stackslib/src/clarity_vm/tests/costs.rs	Replace ad-hoc epoch transition sequences with shared helper; tighten expected default cost-version checks.
stackslib/src/clarity_vm/tests/analysis_costs.rs	Adjust genesis/transition burn-state usage so cost tracker loads the intended boot cost contract from MARF.
stackslib/src/chainstate/stacks/tests/block_construction.rs	Update mempool-walk tests to use the simplified chainstate instantiation helper.
stackslib/src/chainstate/stacks/db/transactions.rs	Update transaction-processing tests to use chainstate helpers that predeploy all costs-N contracts when iterating over multiple epochs.
stackslib/src/chainstate/stacks/db/mod.rs	Add TestChainstateBuilder, deploy-all-costs helper, new instantiation variants, and sanitize chainstate_path().
changelog.d/improve-clarity-vm-tests.changed	Add changelog entry for the test harness improvements.

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