Testing

Test pyramid, consumer-driven contracts, Pact, component/integration/E2E testing; scope vs size distinction, test double fidelity hierarchy, user journey tests, formal verification with TLA+; EDM topology testing, integration testing strategies, event data sourcing

Full classification taxonomy; priority tiers; enterprise fitness functions; mechanism and concern taxonomies; fitness function testing pyramid (triggered/continuous × atomic/holistic → three pyramid layers); ISO 25010 quality attribute anchoring

definition, prerequisites, experiment design, injection types (Chaos Monkey/Latency Monkey/FIT), targeting strategy, automation and moderation, disaster simulations; theoretical foundations (drift into failure, regulator paradox, antifragility); complex systems foundations (accidental vs essential complexity, emergent failures, composability of safety); Netflix origin story; Chaos Maturity Model

*Chaos Engineering: System Resiliency in Practice* — Rosenthal & Jones (eds.); complex systems theory, Five Advanced Principles, Game Days, LDFI, Chaos Maturity Model, Continuous Verification, Security Chaos Engineering, organisational/human factors

Stateless retraining vs stateful training (fine-tuning); four stages of continual learning maturity; champion/challenger pattern; test in production methods (shadow deployment, A/B testing, canary release, interleaving experiments, bandits, contextual bandits); data freshness value; continuous ML challenges (feedback loops, emergency response, stable A/B baselines)

Fitness function automation; stages, fan-in/fan-out; CD vs CDP; cycle time as business metric; zero-downtime deployment (four phases: prepare/drain/apply/start); expand/contract relational schema pattern; trickle-then-batch schemaless migration; canary group evaluation; immutable infrastructure; EDM deployment patterns

Dynamic configuration (config store, runtime re-read); feature flags (progressive rollout, A/B testing, kill switch, deployment-release decoupling); operational triad: monitor → observe → manage

Correctness verification: both implementations run per request; old result returned; GitHub Scientist; dark launching vs canary vs parallel run; progressive delivery

Zero-MTTR via pre-production testing; traditional test hierarchy; production tests (config tests, stress tests, canary); production probes; barrier defence pattern; configuration file risk management