8bit.tr Journal
LLM Regression Testing: Preventing Silent Quality Drops
How to build regression suites that catch quality drops across prompts, models, and retrieval systems.
Why LLMs Regress Easily
Small prompt changes can shift behavior in unexpected ways.
Without regression tests, issues show up in production first.
Building High-Signal Test Sets
Focus on real user flows and high-impact tasks.
Include adversarial and edge-case prompts.
Metrics Beyond Accuracy
Track refusal correctness, factuality, and citation quality.
Add latency and cost checks to catch operational regressions.
Automation in CI
Run regressions on every model, prompt, or retriever change.
Block releases when critical metrics drop.
Human Review Loops
Automated metrics are not enough for ambiguous tasks.
Use a small reviewer pool to validate borderline cases.
Regression Suite Design
Prioritize tests that represent revenue-critical user flows.
Include retrieval failures, tool errors, and formatting issues.
Store expected outputs with tolerances for acceptable variance.
Rotate tests to avoid overfitting to a static suite.
Tag tests by domain so failures can be routed quickly.
Track coverage across languages and locales.
Maintain a gold set for core behaviors that must not change.
Review failed cases monthly to keep the suite current.
Release Gatekeeping
Set pass thresholds for quality, latency, and cost before rollout.
Run regressions on staging traffic to reflect real inputs.
Use canary deploys to catch surprises before full release.
Automate rollback when critical metrics drop below thresholds.
Require sign-off for changes that affect high-risk workflows.
Track regression trends to identify recurring weak spots.
Publish test results alongside release notes for transparency.
Keep a manual override process for emergency fixes.
Define severity levels so failures are triaged consistently.
Include cross-team reviewers for critical system changes.
Schedule freeze windows to stabilize releases during peak traffic.
Capture regression baselines for each model and prompt version.
Track escape rates where failing changes reach production.
Add change risk scores to prioritize deeper review.
Use feature flags to isolate new behaviors safely.
FAQ: Regression Testing
How big should the suite be? Start with 50-100 cases and grow.
Can I reuse benchmarks? Yes, but add product-specific tasks.
What is the quickest win? Automate a small critical-path suite.
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