@kensio/part-factory-test-data

An agent skill for building test data with Part Factory (@kensio/part-factory), a small typed object factory library.

The package README is the authority on the API. This skill covers which factory to reach for, when a mapped factory earns its place, and where factories should live.

Install

Into any agent that reads SKILL.md:

npx @kensio/skills add part-factory-test-data

That copies the skill directory into .agents/skills/, where Codex, Cursor, Copilot, Gemini CLI and the other implementations of the specification look for one. Pass --agent claude for .claude/skills/, --agent copilot for .github/skills/, and --user to install it for every project at once.

Claude Code also takes it as a plugin:

claude plugin marketplace add KensioSoftware/kensio.ai
claude plugin install part-factory-test-data@kensio

Or pin it in a repository as a dependency:

npm install @kensio/part-factory-test-data

Every skill is also published as a zip on each release, for a machine with no npm reach. Unzip it into .agents/skills/ and it is installed.

What it covers

Which factory to reach for. StaticFactory for fixed defaults. DynamicFactory when the defaults have to be generated fresh, paired with faker, which is what gives tests their isolation. VariantFactory for a named variation of a base factory, when the variation is worth a name in the test. MappedFactory when the output shape differs from the parts you want to override.

When a mapped factory earns its place. The map should be a real transformation, such as parts to an encoded form body, or front matter parts to a file as written on disk. If the map is copying fields across into an object of the same shape, you wanted a DynamicFactory.

Call the factory directly. make(overrides) already is that function, and it does the job better, since its overrides are partial all the way down the nested structure where a spread replaces a nested object whole. A wrapper doing more than passing overrides through is a signal that the factory is the wrong shape, or that the output type is fighting you.

Factories belong beside the type they construct. A library defining an event or message shape should export a factory for it, so consumers never hand-roll the literal. The example the skill works through is an AWS Lambda function URL invocation event in payload format 2.0: around thirty lines of which two matter to any test. Hand-writing it in three files gives three copies that drift, and it carries a trap, because the path is in the event twice, as rawPath and as requestContext.http.path. A test that sets one and not the other passes against a handler reading the field the test set, and fails in production against the same handler reading the other one. A MappedFactory sets it once.

Related skills

• isolated-testing-style is the general argument for keeping setup out of test bodies, and for taking isolation from randomised data.
• yulin-aws-simulation covers the AWS simulator those tests run against.

Part of kensio.ai. Licensed under the Apache License 2.0. See the LICENSE in the repository root.