This was originally published on rollgate.io/blog/how-we-test-rollgate .

The Testing Problem No One Talks About

Building a feature flag platform means building something that sits in the critical path of every request your customers serve. If a flag evaluation returns the wrong result, your customer's checkout page shows the wrong UI. If the SDK crashes, your customer's app crashes. If the SSE connection drops, flags go stale.

The testing surface is enormous:

13 SDKs across 7 languages — React, Vue, Angular, Svelte, Node.js, Go, Python, Java, .NET, Flutter, React Native, Browser

A backend API handling flag evaluation in ~200μs P99

Real-time streaming via Server-Sent Events to thousands of concurrent connections

Consistent hashing that must produce identical results across every SDK

I built Rollgate solo over the past year.…