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arXiv · 2608.18039

The Polyglot's Dilemma: Conformance Testing a Dozen Specs in as Many Languages

A. Jesse Jiryu Davis·Jeremy Mikola·Jeff Yemin
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Abstract

MongoDB maintains client libraries in a dozen programming languages, used by tens of thousands of organizations and millions of developers. Most are implemented natively rather than as wrappers around a shared core. Ensuring consistent behavior across these libraries, comprising millions of lines of code, is hard but essential. Over eleven years, we developed a specification-based testing approach: tests are written once in YAML and executed by language-specific interpreters for each library. We describe the evolution from many ad-hoc formats to a Unified Test Format, which allowed us to delete over 22,000 lines of test code. The rate of nonconformance bugs fell up to 86% in drivers that adopted YAML tests (though results varied). We report lessons learned about declarative test design, test architecture, schema evolution, and the limits of unification.

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A. Jesse Jiryu Davis, Jeremy Mikola, Jeff Yemin. 2026-08-18. The Polyglot's Dilemma: Conformance Testing a Dozen Specs in as Many Languages. https://arxiv.org/abs/2608.18039

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