Test Isolation Fix Skill

Discovery

Before touching anything, run the tests in these modes to diagnose the isolation class:

# 1. Reverse order — catches forward-only order dependencies
npx jest --testSequencer ./reverse-sequencer.js

# 2. Random order (jest-random-sequencer or --randomize in Vitest)
npx vitest --sequence.shuffle

# 3. Single test in isolation
npx jest --testPathPattern="failing.test.ts" --runInBand

# 4. Full suite with --runInBand (single thread) vs default (parallel workers)
npx jest --runInBand