--- title: Api Regression Testing: Catch Breaking Changes Early description: API regression testing re-runs tests after each code change so existing endpoints keep returning what clients expect. A solid setup checks response shapes,... canonical: https://daily.dev/posts/api-regression-testing-catch-breaking-changes-early-8ksh9xzig twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Api Regression Testing: Catch Breaking Changes Early | daily.dev og:description: API regression testing re-runs tests after each code change so existing endpoints keep returning what clients expect. A solid setup checks response shapes,... og:url: https://daily.dev/posts/api-regression-testing-catch-breaking-changes-early-8ksh9xzig og:image: https://api.daily.dev/og/posts/8kSH9XZIg.png og:image:alt: Api Regression Testing: Catch Breaking Changes Early og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # Api Regression Testing: Catch Breaking Changes Early **[Ruby Flow](https://daily.dev/sources/rubyflow)** · 14 min read · 0 upvotes · 0 comments ## Summary API regression testing re-runs tests after each code change so existing endpoints keep returning what clients expect. A solid setup checks response shapes, auth, and latency, mocks external dependencies, and runs a fast suite on pull requests with the full suite nightly. Breaking changes include renamed fields, type changes, required-field additions, and status code changes; adding a new response enum value also 'often' breaks strict clients. Keploy records real API traffic to generate tests and mocks automatically, while tools like Schemathesis, oasdiff, Pact, GoReplay, WireMock, and k6 cover spec validation, contract testing, live traffic replay, mocking, and performance gates respectively. A worked example shows a renamed total_amount field failing a replayed test in CI. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Questions this post answers ### Does adding a new value to a response enum count as a breaking API change? Often, yes. Adding an enum value looks additive but clients with strict enum validation will reject the unrecognized value. This is a commonly overlooked breaking change compared to obvious ones like removing a field or changing a status code, since most teams only watch for removals and type changes. _Developers auditing API changes before a release can track breaking-change nuances like this via daily.dev._ ### What's the difference between API regression testing and contract testing? Contract testing checks that a provider still meets expectations its consumers have explicitly written down, using tools like Pact. API regression testing is broader: it verifies behavior, error handling, workflows, and performance against a recorded baseline, catching issues contract testing wouldn't cover. Many teams run both together for full coverage. _Teams deciding how to layer their API test suite can compare these approaches on daily.dev._ ### How do I mask timestamps, UUIDs, and tokens in API regression tests so they don't cause false failures? Mask or ignore dynamic fields like timestamps, UUIDs, session tokens, and request IDs before comparing responses, since a raw comparison fails every run otherwise. For fields where only the format matters, validate the format instead of the exact value. JSON-path ignore rules can exclude specific fields like generatedAt, but keep that list short since every ignored path hides a potential regression. _Engineers wiring up snapshot comparisons can find practical noise-handling patterns like this on daily.dev._ ## Similar posts on daily.dev - [How Open-Source Automation Tools Handle the Testing Problem That Cloud-Native Independent Deployment Creates](https://daily.dev/posts/how-open-source-automation-tools-handle-the-testing-problem-that-cloud-native-independent-deployment-ejpubd1uw) · Container Journal · 0 upvotes · 0 comments - [How Independent Service Deployments Expose the Limits of Conventional Regression Testing Tools](https://daily.dev/posts/how-independent-service-deployments-expose-the-limits-of-conventional-regression-testing-tools-bxfiuoiww) · DevOps.com · 0 upvotes · 0 comments - [Your Python Tests Are Passing. Your APIs Are Not Doing What They Say](https://daily.dev/posts/your-python-tests-are-passing-your-apis-are-not-doing-what-they-say-noevwdkoz) · Medium · 0 upvotes · 0 comments - [Why Cloud-Native Software Testing Requires Rethinking What a Passing Test Actually Means](https://daily.dev/posts/why-cloud-native-software-testing-requires-rethinking-what-a-passing-test-actually-means-yui7y8pjp) · Cloud Native Now · 0 upvotes · 0 comments - [The Regression Testing Habit That Changed How I Think About Shipping Code](https://daily.dev/posts/the-regression-testing-habit-that-changed-how-i-think-about-shipping-code-2dtsz5lot) · Code Like A Girl · 1 upvotes · 0 comments --- Tags: [#cicd](https://daily.dev/tags/cicd), [#openapi](https://daily.dev/tags/openapi) [View this post on daily.dev](https://daily.dev/posts/api-regression-testing-catch-breaking-changes-early-8ksh9xzig) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"Api Regression Testing: Catch Breaking Changes Early","url":"https://daily.dev/posts/api-regression-testing-catch-breaking-changes-early-8ksh9xzig","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/api-regression-testing-catch-breaking-changes-early-8ksh9xzig"},"datePublished":"2026-10-30T11:53:52.028Z","dateModified":"2026-10-30T12:05:27.917Z","description":"API regression testing re-runs tests after each code change so existing endpoints keep returning what clients expect. 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