feat(test-specs): Test mutators

[marioevz]

🗒️ Description

Introduce a spec-test mutator framework that lets fill apply systematic mutations to existing spec tests so we can hunt for edge cases without writing new tests. Mutators are fork-gated: each fork declares which mutators it supports via BaseFork.spec_test_mutators(), and the user opts in per fill invocation.

Usage

fill ... --test-mutators=EIP_7702_ALL_CONTRACTS_AS_DELEGATIONS
fill ... --test-mutators=all

The value selected for a given test is the intersection of what the user requested with what the test's fork supports — so requesting a mutator on a fork that doesn't enable it is a no-op rather than an error, and tests under a fork range get mutated only on the forks where the mutation is meaningful.

First mutator: EIP_7702_ALL_CONTRACTS_AS_DELEGATIONS (Prague+)

Every pre.deploy_contract(...) call is rewritten so that:

1. The original bytecode is placed in a separate account.
2. The address returned to the test is a delegated EOA (0xef0100 || <code-address>) pointing at that account.

This stresses the EIP-7702 delegation path against the full body of existing state/blockchain tests. Edge cases surfaced this way are expected to be promoted into standalone tests as a follow-up — the flag is an exploration aid, not part of regular fill runs.

🔗 Related Issues or PRs

N/A.

✅ Checklist

• All: Ran fast static checks to avoid unnecessary CI fails, see also Code Standards and Enabling Pre-commit Checks:

  just static

• All: PR title adheres to the repo standard - it will be used as the squash commit message and should start type(scope):.
• All: Considered updating the online docs in the ./docs/ directory.
• All: Set appropriate labels for the changes (only maintainers can apply labels).
• Tests: Ran mkdocs serve locally and verified the auto-generated docs for new tests in the Test Case Reference are correctly formatted.
• Tests: For PRs implementing a missed test case, update the post-mortem document to add an entry the list.
• Ported Tests: All converted JSON/YML tests from ethereum/tests or tests/static have been assigned @ported_from marker.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.94%. Comparing base (b3f5df5) to head (5ff1185).

Additional details and impacted files

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##           forks/amsterdam    #2860   +/-   ##
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  Coverage            86.94%   86.94%           
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  Files                  586      586           
  Lines                35777    35777           
  Branches              3363     3363           
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  Hits                 31106    31106           
  Misses                4012     4012           
  Partials               659      659           

Flag	Coverage Δ
unittests	86.94% <ø> (ø)

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[felix314159]

afaik you mainly intend this feature to be used with fill, but when you run execute remote with --test-mutators=EIP_7702_ALL_CONTRACTS_AS_DELEGATIONS it will accept the argument but then silently not mutate? it is a bit dangerous/misleading and we should try to have fill and execute be consistent with each other whenever possible

[felix314159]

the new flag --test-mutators is completely missing from fill --help.

and when you use uv run fill --pytest-help it does show up, but it is useless because it does not tell u which TEST_MUTATORS actually exist, e.g. currently u get

Arguments to specify spec test mutators:                                 
  --test-mutators=TEST_MUTATORS                                                                                                                    
                        Parametrize spec tests with the given comma-separated list of mutators.