Vitest Unit & Integration Testing

What it does

Vitest Unit & Integration Testing is a Cursor skill: a SKILL.md playbook that AgenticKit installs at .cursor/skills/testing-vitest. Cursor's agent loads it when the task matches the skill description, instead of stuffing the same rules into every chat.

Unit and integration testing with Vitest for TypeScript functions, API route handlers, business logic calculations, and database mocks.

Fast unit testing, mock fixtures, edge cases, and code coverage. The file is domain knowledge, not a slash macro. You do not type it. The agent reads it when the job is testing vitest.

Why it exists

Default Cursor has no memory of how your team ships code, schema, and tests. Founders paste the same conventions into chat, then watch the model drift on the next turn. This skill exists so those conventions live on disk and load only when relevant.

It ships in the Engineering Kit. It is wired to the Test Automation Engineer (test-automator) and Root Cause Debugger (debugger) agents. It is wired to the /ship: End-to-End Feature Pipeline Shipper and /fix: Automated Bug & Exception Debugger commands. That graph is the point: the skill is the standard, the agent is the role, the command is the trigger.

When to use it

• Use Vitest Unit & Integration Testing when the work is specifically about fast unit testing, mock fixtures, edge cases, and code coverage.
• Load it before a long session that will touch this surface more than once. A one-line edit does not need the full playbook.
• Use it on production SaaS work (multi-tenant apps, paid features, anything that will be reviewed) rather than a throwaway prototype.

When not to use it

• Do not treat the skill as a replacement for a slash command. Skills teach. Commands run a pipeline.
• Do not paste the whole SKILL.md into chat. If Cursor is not loading it, fix the description or invoke the matching command.
• Do not use it as a generic 'write better code' rule. Scope is this domain only.

Example workflow

1. Install the Engineering Kit so .cursor/skills/testing-vitest lands in the repo.
2. Open a new Cursor agent chat pointed at the files this skill governs.
3. Ask the Test Automation Engineer (test-automator) to read the skill, or run /ship: End-to-End Feature Pipeline Shipper.
4. Review the first artifact against the practices below. If it violates one, stop and correct the file. Do not prompt 'just finish it'.
5. Commit the skill-guided files with the rest of the slice so the next session inherits the same standard.

Example usage

Example prompt: "Read .cursor/skills/testing-vitest and apply it to this change. Do not invent extra conventions."

Or trigger the pipeline: /ship: End-to-End Feature Pipeline Shipper. That command is written to load this skill.

Check the output against: Co-locate test files alongside source files (*.test.ts or *.spec.ts)

Example output

• The skill itself does not write a single output file. It changes what the agent is allowed to produce in code, schema, and tests.
• When you run /ship: End-to-End Feature Pipeline Shipper, expect repo files plus notes under docs/, not a chat-only answer.

Best practices

• Co-locate test files alongside source files (*.test.ts or *.spec.ts)
• Mock external HTTP requests with Mock Service Worker (MSW)
• Test boundary edge cases (null inputs, expired tokens, network timeouts)
• Aim for 90%+ code coverage on core domain business calculations

Common mistakes

• Ignoring "Co-locate test files alongside source files (*.test.ts or *.spec.ts)" and hoping a later prompt will clean it up.
• Copying the skill into .cursor/rules as always-on. That burns context and fights Cursor's load-on-match design.
• Running two overlapping skills that contradict each other in the same turn.
• Letting the agent skip tests or types because 'the skill is about architecture'.