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Agent skill

Fill Tests

by ethereum in ethereum/execution-specs

Fill test fixtures with the repository fill command. An agent skill from ethereum/execution-specs.

CC0-1.0Auto-check passedTesting & QA

Install Fill Tests

skills CLI
$ npx skills add ethereum/execution-specs --skill fill-tests -a claude-code

Project install by default; add -g for ~/.claude/skills/.

GitHub CLI
$ gh skill install ethereum/execution-specs fill-tests --agent claude-code

Project scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).

Manual copy
$ git clone --depth 1 https://github.com/ethereum/execution-specs.git skills-src && mkdir -p .claude/skills && cp -r skills-src/.agents/skills/fill-tests .claude/skills/fill-tests && rm -rf skills-src

Use ~/.claude/skills/ instead of .claude/skills for a personal install. The folder must contain SKILL.md.

Claude Code skills documentation · loads skills from .claude/skills/

Facts

Skill name
fill-tests
GitHub stars
1.2k
Token cost
~793 tokens
SKILL.md length
314 words
Files
1
Skills in repo
13
Repo updated
First seen
Licence
CC0-1.0

At a glance

Fill test fixtures with the repository fill command. An agent skill from ethereum/execution-specs.

  • Tasks that involve Test data and fixtures
  • SKILL.md covers Basic Usage, Key Flags, Debugging and Watch Mode, plus 3 more sections
  • Calls uv and just

What it does

Fill Tests is an agent skill from ethereum/execution-specs. Fill test fixtures with the repository fill command.

Its SKILL.md is about 790 tokens, which your agent loads only when the skill is triggered. It is a single SKILL.md file with no bundled scripts.

It sits in Testing & QA, covering Test data and fixtures. It works with Ethereum and pytest. The repository describes itself as: Specification for the Execution Layer. Tracking network upgrades. The licence is CC0-1.0.

When your agent uses it

  • Tasks that involve Test data and fixtures

Example prompts

  • “/fill-tests”

Requirements

  • Python 3

What it can do on your machine

Read from SKILL.md and the folder at commit dc6d1a5. It shows what the files ask for, not the result of running them.

  • Tool permissions

    Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.

    From allowed-tools in the SKILL.md frontmatter.

  • Runs code

    Shell commands in SKILL.md call:

    • uv
    • just

    From the folder's file list and the shell code blocks in SKILL.md.

  • Network

    No URLs in SKILL.md. Its commands use uv, which can reach the network depending on how they are called.

    From URLs in SKILL.md, links to its own repository left out.

  • Credentials

    Names no API keys, tokens, secrets or passwords.

    From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

Fill Tests loads about 793 tokens when it runs. Until then it costs about 16 tokens; SKILL.md has 314 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it
~16
When it runs · the whole SKILL.md, loaded when a task matches
~793

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Auto-check passed

The automated check found no risky patterns in SKILL.md.

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

The full file from ethereum/execution-specs at commit dc6d1a5, republished under its CC0-1.0 licence (© ethereum). 314 words, ~793 tokens.

Download SKILL.mdSave it as .claude/skills/fill-tests/SKILL.md (or your agent's skills folder).
name
fill-tests
description
Fill test fixtures with the repository fill command.

Fill Tests

CLI reference for the fill command. Run this skill before filling test fixtures. The fill command is pytest-based — all standard pytest flags work.

Basic Usage

bash
uv run fill tests/                                    # Fill all tests
uv run fill tests/cancun/ --fork Cancun               # Specific fork
uv run fill tests/path/to/test.py -k "test_name"      # Specific test
uv run fill tests/osaka/ --until Osaka                 # Up to fork (inclusive)
uv run fill --collect-only tests/                      # Dry run: list tests without executing

Key Flags

  • --fork FORK / --until FORK — target specific fork or range. The default set stops at the last deployed fork, so a fork under development needs one of these.
  • --output DIR + --clean — output directory; --clean required when re-filling
  • -k "pattern" — filter tests by name pattern
  • -m "marker" — filter by pytest marker (e.g. -m state_test, -m blockchain_test)
  • -n auto --maxprocesses N — parallel execution (use --dist=loadgroup)
  • --evm-bin PATH — t8n tool; defaults to the in-repo EELS Python spec (src/ethereum/)
  • --verify-fixtures — run geth's evm blocktest over the generated fixtures. The default EELS t8n has no blocktest, so pass a geth binary with --verify-fixtures-bin. For an EELS-side check use just validate-blocks <fixtures_dir>, which is what CI runs.
  • --generate-all-formats — generate all fixture formats (2-phase)

Debugging

  • --evm-dump-dir DIR — dump t8n input/output for debugging
  • --traces — collect execution traces
  • --pdb — drop into debugger on failure
  • -vv — verbose output; -x — stop on first failure; -s — print stdout

Watch Mode

  • --watch — re-run on file changes (clears screen between runs)
  • --watcherfall — same but keeps output history

Benchmark Tests

  • Excluded from a broad tests/ run: include them by targeting a tests/benchmark/... path, or add --include-benchmark when also collecting tests/.
  • Pick a mode (mutually exclusive): --gas-benchmark-values 1,10,100 (millions of gas) or --fixed-opcode-count 1,10,100 (thousands). These parametrize the tests, e.g. ...[fork_Prague-blockchain_test-benchmark-gas-value_1M].
  • Backend is optional: omitting --evm-bin runs the slow in-repo EELS Python spec; --evm-bin=evmone or --evm-bin=evm (geth, used by just bench-gas) are faster.
  • Stateful benchmarks (tests/benchmark/stateful/) are filled by the separate fill-stateful command against a live client snapshot and produce BlockchainEngineStatefulFixture; see docs/filling_tests/fill_stateful.md.

Fixture Formats

One test function auto-generates multiple formats: StateFixture, BlockchainFixture, BlockchainEngineFixture. --generate-all-formats adds the pre-alloc-group format BlockchainEngineXFixture through a 2-phase run (--generate-pre-alloc-groups, then --use-pre-alloc-groups); --single-fixture-per-file writes each fixture to its own JSON file.

References

See docs/filling_tests/ for detailed documentation.

© ethereum, CC0-1.0. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

Just SKILL.md in .agents/skills/fill-tests of ethereum/execution-specs.

Open the folder on GitHubat commit dc6d1a5

Compare with similar skills

Fill Tests next to the 5 skills that share the most tags, products or categories with it. Stars are the repository's; “used in” counts other GitHub owners with a copy.

Fill Tests compared with similar skills
SkillStarsUsed inTokensAuto-checkLicenceRepo updated
Fill Tests this skillethereum/execution-specs1.2k—~793Automated safety check: PassCC0-1.0
Robotics Testingarpitg1304/robotics-agent-skills369—~4.7kAutomated safety check: PassApache-2.0
Agent-Core Python TestingopenJiuwen-ai/agent-core446—~2.3kAutomated safety check: PassApache-2.0
Test Patternsrohitg00/skillkit1.5k—~1.8kAutomated safety check: PassApache-2.0
Python Testing Strategiesc0x12c/ai-toolkit106—~747Automated safety check: PassNone
FillleanEthereum/leanSpec143—~202Automated safety check: PassMIT

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Works with

Categories

Questions about Fill Tests

What does Fill Tests do?

Fill test fixtures with the repository fill command. An agent skill from ethereum/execution-specs. Fill Tests is an agent skill from ethereum/execution-specs. Fill test fixtures with the repository fill command.

When should I use Fill Tests?

Fill Tests fits situations like: tasks that involve Test data and fixtures.

How do I install Fill Tests in Claude Code?

Run `npx skills add ethereum/execution-specs --skill fill-tests -a claude-code`. Or copy the skill folder (.agents/skills/fill-tests in ethereum/execution-specs) into .claude/skills/fill-tests in your project. Claude Code loads it when a task matches its description.

How do I install Fill Tests in Codex?

Run `npx skills add ethereum/execution-specs --skill fill-tests -a codex`. Or copy the skill folder (.agents/skills/fill-tests in ethereum/execution-specs) into .agents/skills/fill-tests in your project. Codex loads it when a task matches its description.

Can I use Fill Tests in Cursor, Gemini CLI or GitHub Copilot?

Cursor, Gemini CLI, GitHub Copilot and OpenCode also load SKILL.md folders. With the skills CLI, run `npx skills add ethereum/execution-specs --skill fill-tests -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/fill-tests, .gemini/skills/fill-tests, .github/skills/fill-tests and .opencode/skills/fill-tests in your project.

What does Fill Tests need to run?

Going by SKILL.md and its folder, Fill Tests needs the command-line tools its instructions call (uv and just). Our summary lists: Python 3.

Does Fill Tests access the network?

SKILL.md contains no URLs. Its commands use uv, which can reach the network depending on how they are called. This is read from the text; nothing was executed.

Is Fill Tests safe to install?

Our automated static check of SKILL.md found no risky patterns, such as piping downloads into a shell, reading credential files or hidden Unicode. It is not a guarantee. Review the folder before installing.

What licence does Fill Tests use?

Fill Tests is published under the CC0-1.0 licence (the repository's licence). It allows redistribution, so the full SKILL.md is shown on this page.

How many tokens does Fill Tests use?

About 793 tokens (SKILL.md is roughly 3.2k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full.

What are the alternatives to Fill Tests?

Skills that share tags, products or a category with Fill Tests: Robotics Testing (arpitg1304/robotics-agent-skills, 369 stars), Agent-Core Python Testing (openJiuwen-ai/agent-core, 446 stars), Test Patterns (rohitg00/skillkit, 1.5k stars) and Python Testing Strategies (c0x12c/ai-toolkit, 106 stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains Fill Tests?

ethereum (a GitHub organization) maintains it in ethereum/execution-specs, which has 1,195 GitHub stars. The repository holds 13 skills in this directory. The repository was last updated on October 8, 2026.

Source: ethereum/execution-specs on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.