test-regression-design

name	test-regression-design
description	Design or update regression coverage for autodarts-xconfig. Use when a bug fix, feature change, or refactor needs tests at the domain, runtime, config, or DOM harness layer. Do not use for release-only work or README-only edits.

Goal

Design tests that lock in intended behavior and prevent repeated regressions.

Guardrails

• tests should describe behavior, not implementation trivia
• choose the narrowest effective layer that proves the contract
• include at least one test that reproduces the old bug or a close equivalent

Workflow

1. Identify the regression class

Classify the failure as:

• semantic or domain error
• runtime mapping or lifecycle error
• DOM shape or observer error
• config or defaults drift
• integration mismatch between modules

2. Pick the narrowest effective test layer

Prefer:

• domain tests for rules, normalization, ordering, ownership, perspective, and scoring
• runtime tests for snapshot mapping, lifecycle, rerender rules, and observer behavior
• harness tests for DOM shape, merged rows, node replacement, and mount churn

3. Capture the failure mode and edge conditions

Where useful, cover:

• noisy or partial input
• repeated rerenders
• swapped ownership or order
• unchanged semantic state with replaced DOM nodes
• alternate mode variants
• fallback behavior

Output requirements

A valid result from this skill must:

• add or update tests near the correct layer
• protect the changed behavior from regression
• use names that explain the behavioral contract
• avoid shallow tests that only restate the code