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Agent skill

Testing Core Processors

by mastra-ai in mastra-ai/mastra

A skill your agent uses when writing or debugging integration tests for error processors in packages/core/src/processors/.

Custom licenceAuto-check passedTesting & QA

Install Testing Core Processors

skills CLI
$ npx skills add mastra-ai/mastra --skill testing-core-processors -a claude-code

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

GitHub CLI
$ gh skill install mastra-ai/mastra testing-core-processors --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/mastra-ai/mastra.git skills-src && mkdir -p .claude/skills && cp -r skills-src/.agents/skills/testing-core-processors .claude/skills/testing-core-processors && 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
testing-core-processors
GitHub stars
29k
Token cost
~1.1k tokens
SKILL.md length
218 words
Files
1
Skills in repo
44
Repo updated
First seen
Licence
Custom licence

At a glance

A skill your agent uses when writing or debugging integration tests for error processors in packages/core/src/processors/.

  • Works in 3 steps: Happy path: Processor catches the target… → Control test: Same scenario without the… → Selectivity test: Processor ignores…
  • Debugging integration tests for error processors in packages/core/src/processors/
  • SKILL.md covers Prerequisites, Mock Model Pattern, Test Structure and Passing Messages with Tool Calls, plus 2 more sections
  • Calls npx and pnpm; needs ANTHROPIC_API_KEY and OPENROUTER_API_KEY

What it does

Testing Core Processors is an agent skill from mastra-ai/mastra. Use when writing or debugging integration tests for error processors in packages/core/src/processors/. Covers the MockLanguageModelV2 pattern for simulating API errors and verifying retry behavior, plus the build prerequisites for focused vitest runs.

Its SKILL.md is about 1.1k 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 Integration testing and Unit testing. It works with Vitest and Vercel AI SDK. The repository describes itself as: Mastra is the modern TypeScript framework for AI-powered applications and agents.

When your agent uses it

  • Debugging integration tests for error processors in packages/core/src/processors/
  • Tasks that involve Integration testing
  • Tasks that involve Unit testing

Example prompts

  • “/testing-core-processors”

Requirements

  • Node.js
  • A credential in ANTHROPIC_API_KEY
  • A credential in OPENROUTER_API_KEY

Workflow steps

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

  1. Happy path: Processor catches the target error, modifies messages, retries successfully
  2. Control test: Same scenario without the processor — error propagates
  3. Selectivity test: Processor ignores unrelated errors (e.g. rate limit 429)

What it can do on your machine

Read from SKILL.md and the folder at commit 79ea2ae. 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:

    • npx
    • pnpm

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

  • Network

    No URLs in SKILL.md. Its commands use npx and pnpm, 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 these keys or tokens, usually read from environment variables:

    • ANTHROPIC_API_KEY
    • OPENROUTER_API_KEY

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

Context cost

Testing Core Processors loads about 1.1k tokens when it runs. Until then it costs about 69 tokens; SKILL.md has 218 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it
~69
When it runs · the whole SKILL.md, loaded when a task matches
~1.1k

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

Its licence (Custom licence) doesn't allow us to republish the file, so here is its outline and opening line. It has 218 words (~1,059 tokens).

“How to write integration tests for error processors in packages/core/src/processors/.”

— opening of SKILL.md by mastra-ai, Custom licence
name
testing-core-processors

Read the full SKILL.md on GitHub

Files

Just SKILL.md in .agents/skills/testing-core-processors of mastra-ai/mastra.

Open the folder on GitHubat commit 79ea2ae

Compare with similar skills

Testing Core Processors 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.

Testing Core Processors compared with similar skills
SkillStarsUsed inTokensAuto-checkLicenceRepo updated
Testing Core Processors this skillmastra-ai/mastra29k—~1.1kAutomated safety check: PassCustom licence
Test Writing WorkflowiOfficeAI/AionUi33k1 repos~1.2kAutomated safety check: PassApache-2.0
Designing TestsCloudAI-X/claude-workflow-v21.4k1 repos~1.5kAutomated safety check: PassMIT
Frontend TestingOhh-889/skyroc7951 repos~2.5kAutomated safety check: PassMIT
Running TestsNangoHQ/nango13k—~876Automated safety check: PassCustom licence
Backend Testingbiersoeckli/QuickStack362—~670Automated safety check: PassGPL-3.0

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Works with

Categories

Questions about Testing Core Processors

What does Testing Core Processors do?

A skill your agent uses when writing or debugging integration tests for error processors in packages/core/src/processors/. Testing Core Processors is an agent skill from mastra-ai/mastra. Use when writing or debugging integration tests for error processors in packages/core/src/processors/.

When should I use Testing Core Processors?

Testing Core Processors fits situations like: debugging integration tests for error processors in packages/core/src/processors/; tasks that involve Integration testing; tasks that involve Unit testing.

How do I install Testing Core Processors in Claude Code?

Run `npx skills add mastra-ai/mastra --skill testing-core-processors -a claude-code`. Or copy the skill folder (.agents/skills/testing-core-processors in mastra-ai/mastra) into .claude/skills/testing-core-processors in your project. Claude Code loads it when a task matches its description.

How do I install Testing Core Processors in Codex?

Run `npx skills add mastra-ai/mastra --skill testing-core-processors -a codex`. Or copy the skill folder (.agents/skills/testing-core-processors in mastra-ai/mastra) into .agents/skills/testing-core-processors in your project. Codex loads it when a task matches its description.

Can I use Testing Core Processors 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 mastra-ai/mastra --skill testing-core-processors -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/testing-core-processors, .gemini/skills/testing-core-processors, .github/skills/testing-core-processors and .opencode/skills/testing-core-processors in your project.

What does Testing Core Processors need to run?

Going by SKILL.md and its folder, Testing Core Processors needs the command-line tools its instructions call (npx and pnpm) and credentials named ANTHROPIC_API_KEY and OPENROUTER_API_KEY. Our summary lists: Node.js; A credential in ANTHROPIC_API_KEY; A credential in OPENROUTER_API_KEY.

Does Testing Core Processors access the network?

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

Is Testing Core Processors 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 Testing Core Processors use?

Testing Core Processors has a licence file (the repository's licence) that doesn't match a standard licence. Read it on GitHub before reusing the skill.

How many tokens does Testing Core Processors use?

About 1.1k tokens (SKILL.md is roughly 4.2k 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 Testing Core Processors?

Skills that share tags, products or a category with Testing Core Processors: Test Writing Workflow (iOfficeAI/AionUi, 33k stars), Designing Tests (CloudAI-X/claude-workflow-v2, 1.4k stars), Frontend Testing (Ohh-889/skyroc, 795 stars) and Running Tests (NangoHQ/nango, 13k stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains Testing Core Processors?

mastra-ai (a GitHub organization) maintains it in mastra-ai/mastra, which has 28,628 GitHub stars. The repository holds 44 skills in this directory. The repository was last updated on October 8, 2026.

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