Tests written before implementation

Red phase described

Green phase described

Refactor phase described

Test file uses beforeEach setup

Tests use mock dependencies

Private helper methods extracted

Jest coverage configured

Coverage thresholds at 80%

Coverage path exclusions

Tests cover both channels

Cache checked first

Single DB query used

JOIN query used

Results cached after DB query

Cache TTL provided

Cache key uses userId

Cache hit test

Cache miss test

Original problem documented

Caching approach documented

CircuitBreaker three states

CircuitBreaker default threshold=5

CircuitBreaker default timeout=60000

Circuit opens on threshold

Circuit half-open reset attempt

Retry exponential backoff

Retry default attempts=3

AppError base class

Typed error subclasses

Operational vs unexpected error handler

Circuit breaker state test

Retry behaviour test