Testing Unit

What it does

When your agent uses it

• Writing unit tests
• Setting up mocks
• Structuring test data
• Optimizing test speed

Example prompts

• “/testing-unit”

Requirements

• Python 3
• Compatibility (from SKILL.md): Claude Code 2.1.277+.
• Pre-approved tools (allowed-tools): Read, Glob, Grep, WebFetch, WebSearch

Workflow steps

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

1. 1AAA structure: Every test MUST follow Arrange-Act-Assert. Use // Arrange, // Act, // Assert comments for clarity.
2. 2Parametrize, don't duplicate: Use test.each (TypeScript) or @pytest.mark.parametrize (Python) when testing multiple inputs. Never…
3. 3Fixture scoping matters: Use scope="function" (default) for mutable data. Use scope="module" or scope="session" ONLY for expensive…
4. 4Speed target: Each unit test should run under 100ms. If it's slower, you're likely hitting I/O — mock it.
5. 5Mock at the network level: Use MSW (TypeScript) or VCR.py (Python) to intercept HTTP at the network layer. Never mock fetch/axios/requests…

What it can do on your machine

Read from SKILL.md and the folder at commit 1f8d8f3. It shows what the files ask for, not the result of running them.

• Tool permissions

  Pre-approves these tools, so the agent can use them without asking each time:

  • Read
  • Glob
  • Grep
  • WebFetch
  • WebSearch

  From allowed-tools in the SKILL.md frontmatter.

• Runs code

  Ships 1 file in scripts/, which the agent can run.

  Shell commands in SKILL.md call:

  • vitest

  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.

• Compatibility

  Claude Code 2.1.277+.

  From compatibility in the SKILL.md frontmatter.

Context cost

Testing Unit loads about 2.4k tokens when it runs, and up to ~6k if it reads all its reference files. Until then it costs about 116 tokens; SKILL.md has 672 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it

~116

When it runs · the whole SKILL.md, loaded when a task matches

~2.4k

With references · SKILL.md plus every file in references/, read only if the agent opens them

~6k

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

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); the scripts in this folder are not scanned.

SKILL.md

The full file from yonatangross/orchestkit at commit 1f8d8f3, republished under its MIT licence (© yonatangross). 672 words, ~2,436 tokens.

name

testing-unit

description

Unit testing patterns for isolated business logic tests — AAA pattern, parametrized tests (test.each, @pytest.mark.parametrize), fixture scoping (function/module/session), mocking with MSW/VCR at network level, and test data management with factories (FactoryBoy, faker-js). Use when writing unit tests, setting up mocks, structuring test data, optimizing test speed, choosing fixture scope, or reducing test boilerplate. Covers Vitest, Jest, pytest.

allowed-tools

Read, Glob, Grep, WebFetch, WebSearch

compatibility

Claude Code 2.1.277+.

license

MIT

context

fork

agent

test-generator

user-invocable

false

disable-model-invocation

false

metadata.category

document-asset-creation

metadata.version

2.1.0

metadata.author

OrchestKit

metadata.complexity

medium

metadata.tags

testing, unit, mocking, msw, vcr, fixtures, factories, vitest-4, aroundEach

import { describe, test, expect, beforeAll, afterEach, afterAll } from 'vitest';
import { http, HttpResponse } from 'msw';
import { setupServer } from 'msw/node';
import { calculateDiscount } from './pricing';

// 1. Pure unit test with AAA pattern
describe('calculateDiscount', () => {
  test.each([
    [100, 0],
    [150, 15],
    [200, 20],
  ])('for order $%i returns $%i discount', (total, expected) => {
    // Arrange
    const order = { total };

    // Act
    const discount = calculateDiscount(order);

    // Assert
    expect(discount).toBe(expected);
  });
});

// 2. MSW mocked API test
const server = setupServer(
  http.get('/api/users/:id', ({ params }) => {
    return HttpResponse.json({ id: params.id, name: 'Test User' });
  })
);

beforeAll(() => server.listen({ onUnhandledRequest: 'error' }));
afterEach(() => server.resetHandlers());
afterAll(() => server.close());

test('fetches user from API', async () => {
  // Arrange — MSW handler set up above

  // Act
  const response = await fetch('/api/users/123');
  const data = await response.json();

  // Assert
  expect(data.name).toBe('Test User');
});

import pytest
from factory import Factory, Faker, SubFactory

class UserFactory(Factory):
    class Meta:
        model = dict
    email = Faker('email')
    name = Faker('name')

class TestUserService:
    @pytest.mark.parametrize("role,can_edit", [
        ("admin", True),
        ("viewer", False),
    ])
    def test_edit_permission(self, role, can_edit):
        # Arrange
        user = UserFactory(role=role)

        # Act
        result = user_can_edit(user)

        # Assert
        assert result == can_edit

test.aroundEach(async (runTest, { db }) => {
  await db.transaction(runTest)  // auto-rollback on test end
})

test('insert user', async ({ db }) => {
  await db.insert({ name: 'Alice' })
  // transaction auto-rolls back — no cleanup needed
})

const fn = vi.fn()
fn.mockThrow(new Error('connection lost'))  // always throws
fn.mockThrowOnce(new Error('timeout'))      // throws once, then normal

const assertPair = vi.defineHelper((a, b) => {
  expect(a).toEqual(b)  // error points to where assertPair() was CALLED
})

// vitest.config.ts
test: {
  tags: {
    unit: { timeout: 5000 },
    flaky: { retry: 3 },
  }
}

vitest --tags-filter="unit and !flaky"
vitest --tags-filter="(unit or integration) and !slow"

AI_AGENT=copilot vitest    # auto-detect agent mode

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

Files

SKILL.md and 22 other files (scripts, references) in src/skills/testing-unit of yonatangross/orchestkit.

• SKILL.md
• checklists/msw-setup-checklist.md
• checklists/test-data-checklist.md
• checklists/vcr-checklist.md
• examples/handler-patterns.md
• references/aaa-pattern.md
• references/factory-patterns.md
• references/msw-2x-api.md
• references/stateful-testing.md
• rules/_sections.md
• rules/data-factories.md
• rules/data-fixtures.md
• rules/data-seeding-cleanup.md
• rules/mocking-msw.md
• rules/mocking-vcr.md
• rules/unit-aaa-pattern.md
• rules/unit-fixture-scoping.md
• … and 6 more

Open the folder on GitHubat commit 1f8d8f3