Agent skill

Write Tests

Write tests for Syncpack using the TestBuilder pattern. An agent skill from JamieMason/syncpack.

MITAuto-check passedTesting & QA

Install Write Tests

skills CLI

$ npx skills add JamieMason/syncpack --skill write-tests -a claude-code

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

GitHub CLI

$ gh skill install JamieMason/syncpack write-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/JamieMason/syncpack.git skills-src && mkdir -p .claude/skills && cp -r skills-src/.claude/skills/write-tests .claude/skills/write-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/

Paste into Claude Code

Install the "write-tests" agent skill from https://github.com/JamieMason/syncpack/tree/main/.claude/skills/write-tests into .claude/skills/write-tests/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "write-tests", then confirm the skill loads.

Claude Code copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

$skill-installer

$skill-installer install https://github.com/JamieMason/syncpack/tree/main/.claude/skills/write-tests

Type this inside Codex. $skill-installer <name> installs a curated skill from openai/skills. The installer writes to $CODEX_HOME/skills (default ~/.codex/skills). Restart Codex if the skill does not show up.

skills CLI

$ npx skills add JamieMason/syncpack --skill write-tests -a codex

Project install goes to .agents/skills/; add -g for ~/.codex/skills/.

GitHub CLI

$ gh skill install JamieMason/syncpack write-tests --agent codex

Project scope by default (.agents/skills/); add --scope user for a personal install.

Manual copy

$ git clone --depth 1 https://github.com/JamieMason/syncpack.git skills-src && mkdir -p .agents/skills && cp -r skills-src/.claude/skills/write-tests .agents/skills/write-tests && rm -rf skills-src

Use ~/.agents/skills/ instead of .agents/skills for a personal install.

Codex skills documentation · loads skills from .agents/skills/

Paste into Codex

Install the "write-tests" agent skill from https://github.com/JamieMason/syncpack/tree/main/.claude/skills/write-tests into .agents/skills/write-tests/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "write-tests", then confirm the skill loads.

Codex copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

skills CLI

$ npx skills add JamieMason/syncpack --skill write-tests -a cursor

Project install goes to .agents/skills/; add -g for ~/.cursor/skills/.

GitHub CLI

$ gh skill install JamieMason/syncpack write-tests --agent cursor

Project scope by default (.agents/skills/); add --scope user for a personal install.

Manual copy

$ git clone --depth 1 https://github.com/JamieMason/syncpack.git skills-src && mkdir -p .cursor/skills && cp -r skills-src/.claude/skills/write-tests .cursor/skills/write-tests && rm -rf skills-src

Use ~/.cursor/skills/ instead of .cursor/skills for a personal install.

Cursor skills documentation · loads skills from .cursor/skills/, .agents/skills/, .claude/skills/, .codex/skills/

Paste into Cursor

Install the "write-tests" agent skill from https://github.com/JamieMason/syncpack/tree/main/.claude/skills/write-tests into .cursor/skills/write-tests/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "write-tests", then confirm the skill loads.

Cursor copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

gemini skills install

$ gemini skills install https://github.com/JamieMason/syncpack.git --path .claude/skills/write-tests

--scope user (default) or --scope workspace; --path is the subfolder of the repo that holds the skill; --consent skips the security confirmation prompt.

skills CLI

$ npx skills add JamieMason/syncpack --skill write-tests -a gemini-cli

Project install goes to .agents/skills/; add -g for ~/.gemini/skills/.

GitHub CLI

$ gh skill install JamieMason/syncpack write-tests --agent gemini-cli

Project scope by default (.agents/skills/); add --scope user for a personal install.

Manual copy

$ git clone --depth 1 https://github.com/JamieMason/syncpack.git skills-src && mkdir -p .gemini/skills && cp -r skills-src/.claude/skills/write-tests .gemini/skills/write-tests && rm -rf skills-src

Use ~/.gemini/skills/ instead of .gemini/skills for a personal install, then run /skills reload.

Gemini CLI skills documentation · loads skills from .gemini/skills/, .agents/skills/

Paste into Gemini CLI

Install the "write-tests" agent skill from https://github.com/JamieMason/syncpack/tree/main/.claude/skills/write-tests into .gemini/skills/write-tests/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "write-tests", then confirm the skill loads.

Gemini CLI copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

GitHub CLI

$ gh skill install JamieMason/syncpack write-tests

Installs for Copilot at project scope by default; add --scope user for a personal install. Preview a skill first with gh skill preview. Needs GitHub CLI 2.90.0 or later (public preview).

skills CLI

$ npx skills add JamieMason/syncpack --skill write-tests -a github-copilot

Project install goes to .agents/skills/; add -g for ~/.copilot/skills/.

Manual copy

$ git clone --depth 1 https://github.com/JamieMason/syncpack.git skills-src && mkdir -p .github/skills && cp -r skills-src/.claude/skills/write-tests .github/skills/write-tests && rm -rf skills-src

Use ~/.copilot/skills/ instead of .github/skills for a personal install. Commit .github/skills so cloud agent and code review can use it.

GitHub Copilot skills documentation · loads skills from .github/skills/, .claude/skills/, .agents/skills/

Paste into GitHub Copilot

Install the "write-tests" agent skill from https://github.com/JamieMason/syncpack/tree/main/.claude/skills/write-tests into .github/skills/write-tests/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "write-tests", then confirm the skill loads.

GitHub Copilot copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

skills CLI

$ npx skills add JamieMason/syncpack --skill write-tests -a opencode

OpenCode documents no install command of its own. Project install goes to .agents/skills/; add -g for ~/.config/opencode/skills/.

GitHub CLI

$ gh skill install JamieMason/syncpack write-tests --agent opencode

Project scope by default (.agents/skills/); add --scope user for a personal install.

Manual copy

$ git clone --depth 1 https://github.com/JamieMason/syncpack.git skills-src && mkdir -p .opencode/skills && cp -r skills-src/.claude/skills/write-tests .opencode/skills/write-tests && rm -rf skills-src

Use ~/.config/opencode/skills/ instead of .opencode/skills for a personal install.

OpenCode skills documentation · loads skills from .opencode/skills/, .claude/skills/, .agents/skills/

Paste into OpenCode

Install the "write-tests" agent skill from https://github.com/JamieMason/syncpack/tree/main/.claude/skills/write-tests into .opencode/skills/write-tests/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "write-tests", then confirm the skill loads.

OpenCode copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

Facts

Skill name: write-tests
GitHub stars: 2.1k
Token cost: ~2.3k tokens
SKILL.md length: 358 words
Files: 2
Skills in repo: 11
Repo updated: Sep 26, 2026
First seen: Oct 7, 2026
Licence: MIT

At a glance

Write tests for Syncpack using the TestBuilder pattern. An agent skill from JamieMason/syncpack.

Works in 4 steps: Read 2-3 tests in the same *_test.rs and… → Write failing test → just test → confirm… → Ask before implementing → …
Adding tests for commands
SKILL.md covers Golden rules, TDD, Quick start and Sub-module organisation, plus 8 more sections
Calls just and cargo

What it does

Write Tests is an agent skill from JamieMason/syncpack. Write tests for Syncpack using the TestBuilder pattern. Use when adding tests for commands, validation logic, or any new functionality. Covers TestBuilder API, assertion patterns, and common test scenarios.

Its SKILL.md is about 2.3k tokens, which your agent loads only when the skill is triggered. The skill folder holds 1 other file (for example `patterns.md`).

It sits in Testing & QA, covering Test generation. It works with npm. The repository describes itself as: Consistent dependency versions in large JavaScript Monorepos. The licence is MIT.

When your agent uses it

Adding tests for commands
Validation logic
Any new functionality

Example prompts

“/write-tests”

Workflow steps

4 steps, taken from the first numbered list in SKILL.md.

Read 2-3 tests in the same *_test.rs and copy the pattern
Write failing test → just test → confirm RED
Ask before implementing
Implement minimal code → GREEN → just format

What it can do on your machine

Read from SKILL.md and the folder at commit 958d306. 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:
- just
- cargo
From the folder's file list and the shell code blocks in SKILL.md.
Network
No URLs in SKILL.md.
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

Write Tests loads about 2.3k tokens when it runs. Until then it costs about 55 tokens; SKILL.md has 358 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it: ~55
When it runs · the whole SKILL.md, loaded when a task matches: ~2.3k

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 JamieMason/syncpack at commit 958d306, republished under its MIT licence (© JamieMason). 358 words, ~2,287 tokens.

Download SKILL.mdSave it as .claude/skills/write-tests/SKILL.md (or your agent's skills folder). This skill also uses 1 other file; get the full folder from GitHub.

name: write-tests
description: Write tests for Syncpack using the TestBuilder pattern. Use when adding tests for commands, validation logic, or any new functionality. Covers TestBuilder API, assertion patterns, and common test scenarios.

Write Tests

Golden rules

Use TestBuilder — never construct Context manually.
Assert with expect(&ctx).to_have_instances(vec![...]) — never index ctx.instances.
Async-first: #[tokio::test] + .run().await is the canonical entry.

TDD

Read 2-3 tests in the same *_test.rs and copy the pattern
Write failing test → just test → confirm RED
Ask before implementing
Implement minimal code → GREEN → just format

Quick start

rust

use {
  crate::{
    instance::{FixableInstance::*, InstanceState, SuspectInstance::*, UnfixableInstance::*, ValidInstance::*},
    test::{
      builder::TestBuilder,
      expect::{expect, ExpectedInstance},
    },
  },
  serde_json::json,
};

#[tokio::test]
async fn pinned_version_replaces_anything_different() {
  let ctx = TestBuilder::new()
    .with_package(json!({
      "name": "package-a",
      "version": "1.0.0",
      "devDependencies": {"foo": "workspace:*"}
    }))
    .with_version_group(json!({
      "dependencies": ["foo"],
      "pinVersion": "1.2.0"
    }))
    .run()
    .await;
  expect(&ctx).to_have_instances(vec![
    ExpectedInstance {
      state: InstanceState::valid(IsLocalAndValid),
      dependency_name: "package-a",
      id: "package-a in /version of package-a",
      actual: "1.0.0",
      expected: Some("1.0.0"),
      overridden: None,
    },
    ExpectedInstance {
      state: InstanceState::fixable(DiffersToPin),
      dependency_name: "foo",
      id: "foo in /devDependencies of package-a",
      actual: "workspace:*",
      expected: Some("1.2.0"),
      overridden: None,
    },
  ]);
}

Sub-module organisation

Group related scenarios under nested modules — see pinned_test.rs, catalog_defs_test.rs:

rust

mod local {
  use super::*;
  #[tokio::test] async fn refuses_to_pin_local_version() { ... }
}

mod normal {
  use super::*;
  #[tokio::test] async fn an_already_pinned_version_is_valid() { ... }
}

mod registry_updates {
  use super::*;
  #[tokio::test] async fn def_marked_outdated_when_registry_has_newer_version() { ... }
}

File location

Test type	Location
Version-group behaviour (pin, ban, ranges …)	`src/version_group/<group>_test.rs`
Catalog discovery wiring	`src/version_group/{catalog,bun_catalog}_test.rs`
Fix mutations	`src/commands/fix_test.rs`
Format pass	`src/visit_formatting/format_test.rs`
Other unit tests	Co-located: `src/foo.rs` ↔ `src/foo_test.rs`

Builder methods

Source of truth: src/test/builder.rs.

Method	Purpose
`.with_package(json!({...}))`	Add one package.json
`.with_packages(vec![...])`	Add many
`.with_version_group(json!({...}))`	Add one version group
`.with_version_groups(vec![...])`	Add many
`.with_semver_group(json!({...}))`	Add a semver group
`.with_config(json!({...}))`	Base config (e.g. `customTypes`, `dependencyGroups`)
`.with_strict(bool)`	Strict mode (Suspect → error)
`.with_subcommand("update")`	Override subcommand (default: `lint`, or `update` if registry set)
`.with_pnpm_catalogs(yaml)`	Inject `pnpm-workspace.yaml`; implies pnpm PM
`.with_bun_catalogs(json!({...}))`	Synthetic Bun root with `/catalog`, `/catalogs/{n}`; implies Bun PM
`.with_bun_workspaces_catalogs(json!({...}))`	Same, nested under `/workspaces/`
`.with_{pnpm,bun,npm,yarn,unknown}_package_manager()`	Force PM detection
`.with_registry_updates(json!({"react":[...]}))`	Mock npm registry; implies subcommand=`update`
`.with_update_target(UpdateTarget::Minor)`	Bound update target
`.run().await` → `Context`	Primary end-to-end (full pipeline through disk + discovery)
`.build()`	Sync, no visit — context-wiring tests
`.build_and_visit_packages()`	Sync + visit_packages — fix tests, older suites
`.build_and_visit_formatting()`	Sync + visit_formatting
`.build_with_registry_and_visit().await`	Sync wiring + async registry mock + visit

Show full SKILL.md (147 more words)Show less

ExpectedInstance fields

rust

ExpectedInstance {
  state: InstanceState::fixable(DiffersToPin),  // valid / fixable / unfixable / suspect
  dependency_name: "react",                     // = `internal_name` (alias-aware)
  id: "react in /dependencies of package-a",    // {dep} in {/path} of {package_or_yaml}
  actual: "17.0.0",                             // raw specifier on disk
  expected: Some("18.0.0"),                     // None = ignore; Some("") = remove
  overridden: None,                             // semver-group override target, if any
}

id location examples:

/dependencies, /devDependencies, /peerDependencies
/version of package-a (local version)
/packageManager, /engines/node
/catalog of pnpm-workspace.yaml, /catalogs/<name> of pnpm-workspace.yaml
/customVersion, /custom/config/version (via customTypes)

Patterns

→ patterns.md: banned, pinned, sameRange, pnpm catalogs, bun catalogs, semver ranges, registry updates.

Fix tests

src/commands/fix_test.rs builds with .build_and_visit_packages() then runs fix::run(ctx, &SilentReporter, &disk). dry_run = true is the default (set by mock::config_from_mock), so is_dirty() and post-fix contents stay observable. Set ctx.config.cli.dry_run = false only when asserting writes through a recording MockDiskIo (see pnpm_fix_writes_yaml_to_disk).

Common mistakes

Wrong	Right
`#[test] fn foo()` + `.run().await`	`#[tokio::test] async fn foo()`
`use crate::instance_state::*`	`use crate::instance::*`
`"pinned": "1.0.0"`	`"pinVersion": "1.0.0"`
`Context { ... }`	`TestBuilder::new()...`
`ctx.instances[0]`	`expect(&ctx).to_have_instances(vec![...])`
`.build()` then check states	`.run().await` (or `.build_and_visit_packages()` for sync)
Missing `SuspectInstance::*` import	Import all 4: `FixableInstance::, ValidInstance::, SuspectInstance::, UnfixableInstance::`

Running

bash

just test                            # all
cargo test pinned_test               # pattern match
cargo test test_name -- --nocapture  # with stdout

Reference tests

src/version_group/banned_test.rs — banned + custom types
src/version_group/pinned_test.rs — sub-modules, semver-group interaction
src/version_group/same_range_test.rs — range satisfaction
src/version_group/catalog_test.rs — pnpm catalogs
src/version_group/bun_catalog_test.rs — bun catalogs (sync .build())
src/version_group/preferred_semver_test.rs — registry updates, update targets

Files

SKILL.md and 1 other file in .claude/skills/write-tests of JamieMason/syncpack.

SKILL.md
patterns.md

Open the folder on GitHubat commit 958d306

Compare with similar skills

Write 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.

Write Tests compared with similar skills
Skill	Stars	Used in	Tokens	Auto-check	Licence	Repo updated
Write Tests this skillJamieMason/syncpack	2.1k	—	~2.3k	Automated safety check: Pass	MIT	11 days ago
Test ScopeGlitterKill/sdl-mcp	490	—	~586	Automated safety check: Pass	Custom licence	16 days ago
Pre Commitwellwelwel/poku	1.2k	—	~728	Automated safety check: Pass	MIT	3 mo ago
Make Git Escrowinternet-court/internet-court-skill	6.4k	1 repos	~922	Automated safety check: Notes	MIT	1 mo ago
Write Testsryokun6/ryos	1.3k	—	~1.7k	Automated safety check: Pass	AGPL-3.0	today
Backend Test Writeraiskillstore/marketplace	430	1 repos	~1.1k	Automated safety check: Pass	None	today

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Questions about Write Tests

What does Write Tests do?

Write tests for Syncpack using the TestBuilder pattern. An agent skill from JamieMason/syncpack. Write Tests is an agent skill from JamieMason/syncpack. Write tests for Syncpack using the TestBuilder pattern.

When should I use Write Tests?

Write Tests fits situations like: adding tests for commands; validation logic; any new functionality.

How do I install Write Tests in Claude Code?

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

How do I install Write Tests in Codex?

Run `npx skills add JamieMason/syncpack --skill write-tests -a codex`. Or copy the skill folder (.claude/skills/write-tests in JamieMason/syncpack) into .agents/skills/write-tests in your project. Codex loads it when a task matches its description.

Can I use Write 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 JamieMason/syncpack --skill write-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/write-tests, .gemini/skills/write-tests, .github/skills/write-tests and .opencode/skills/write-tests in your project.

What does Write Tests need to run?

Going by SKILL.md and its folder, Write Tests needs the command-line tools its instructions call (just and cargo).

Does Write Tests access the network?

SKILL.md contains no URLs. Any network use would come from the scripts or tools the agent runs. This is read from the text; nothing was executed.

Is Write 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 Write Tests use?

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

How many tokens does Write Tests use?

About 2.3k tokens (SKILL.md is roughly 9.1k 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 Write Tests?

Skills that share tags, products or a category with Write Tests: Test Scope (GlitterKill/sdl-mcp, 490 stars), Pre Commit (wellwelwel/poku, 1.2k stars), Make Git Escrow (internet-court/internet-court-skill, 6.4k stars) and Write Tests (ryokun6/ryos, 1.3k stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains Write Tests?

JamieMason (a GitHub user) maintains it in JamieMason/syncpack, which has 2,099 GitHub stars. The repository holds 11 skills in this directory. The repository was last updated on September 26, 2026.

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

Install Write Tests

Facts

At a glance

What it does

When your agent uses it

Example prompts

Workflow steps

What it can do on your machine

Tool permissions

Runs code

Network

Credentials

Context cost

Safety

SKILL.md

Write Tests

Golden rules

TDD

Quick start

Sub-module organisation

File location

Builder methods

ExpectedInstance fields

Patterns

Fix tests

Common mistakes

Running

Reference tests

Files

Compare with similar skills

Similar skills

More from JamieMason/syncpack

Related

Questions about Write Tests