Individual skill

test-data-builder

Builds realistic domain fixtures, factories, and edge-case datasets with the builder pattern and valid defaults, so each test owns exactly the data it asserts on. Use when someone asks "how should I set up test data", "my fixtures broke half the suite", "make a factory for this model", "why is this test flaky only in CI", or a test needs domain objects, seed data, or boundary inputs. Do NOT use when a test needs to fake a network call, database client, clock, or third-party SDK - use mock-stub-designer instead; do NOT use for designing the assertions or test cases themselves - use tdd-expert instead.

skills/test-data-builder/SKILL.md

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Repository last updated: Oct 13, 2026
License: MIT

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claude Repository topic
claude-skills Repository topic
skill-me Repository topic
data Derived category
testing Derived category
data-databases Derived category

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# Test Data Builder

Produce per-test domain data that is realistic, deterministic, and isolated. The costly failure this prevents is the shared fixture file that becomes an append-only god object: one test tweaks a record, three unrelated tests start flaking, and nobody can delete a fixture row because nobody knows who depends on it. Builders with valid defaults make every test self-describing and every failure reproducible.

## Operating procedure

Order matters: defaults must be valid before overrides mean anything, and determinism must be in place before you add realistic randomness.

### Step 1: Gather inputs

Collect before writing a factory. Defaults in parentheses; label guesses as guesses.

1. The domain object(s) under test and their required fields.
2. The stack's factory library (FactoryBot for Ruby, Fishery or test-data-bot for TypeScript, factory_boy for Python, Bogus/AutoFixture for .NET; default: hand-rolled builder if none exists).