Testing Claude Prompt Outputs with Node.js Built-in test Runner

The node:test module in Node 20 and later offers a native way to unit-test LLM prompts without heavy external frameworks. Because models like Claude produce probabilistic output, a small change in wording can break structured responses such as JSON that downstream code depends on. Writing prompt tests guards against regressions after prompt or model changes, documents expected output shapes, and keeps CI pipelines fast. The guide covers the basic test setup, the need to return or await async tests so failures are not silently ignored, and an example that calls Claude through Amazon Bedrock to check the returned JSON.