How do you ensure a cloud-native reference implementation behaves consistently across Python, Go, .NET, JavaScript, Java, and beyond? Discover how the flagd-testbed project validates both the core flagd service and its language-specific integrations through a single, unified test suite. Leveraging Gherkin specifications as behavioral contracts, Testcontainers for real-world integration testing, and Renovate for automated testbed synchronization, this approach delivers reliable feature flagging across diverse environments. Reusable Gherkin steps and clear step mapping streamline bug identification, instantly pinpointing whether failures stem from the core service, language implementations, or integration layers—catching subtle bugs before they reach production. Learn practical strategies for scalable polyglot testing, reusable test specifications, and building infrastructure that grows with your ecosystem. Join us for actionable insights and real-world lessons from the flagd testbed!