Engineering notes on testing, performance and APIs.
Long-form, practical articles with runnable code. Written for engineers and CTOs at SaaS and fintech companies. RSS
Reading performance test results: percentiles, HDR histograms, saturation and Little's Law
How to interpret load test output correctly: why averages mislead, why percentiles cannot be averaged, how to find the saturation point, and how to report results people can act on.
Read the article →API testing · 8 min readIdempotency and race conditions in payment APIs: how to test them properly
A practical guide to Idempotency-Key semantics, duplicate-request scenarios and concurrency testing techniques for payment APIs, with runnable Python and SQL examples.
Read the article →Contract testing · 8 min readContract testing for microservices: Pact vs OpenAPI schema validation
Consumer-driven contracts with Pact and provider-side OpenAPI validation solve different problems. When each fits, how they combine, and a CI setup that blocks breaking changes.
Read the article →Load testing · 9 min readWriting realistic load tests with k6: open vs closed models, arrival rates and coordinated omission
Why most load tests under-report latency, and how to fix that with k6 arrival-rate executors, sensible thresholds, think time and proper correlation.
Read the article →Rather have it checked than read about it?
Short written findings on your API or app, non-intrusive.