--- title: Where did it hide a SwiftUI rendering bug? | daily.dev description: A SwiftUI performance bug went undetected because tests only validated state mutations, not rendering efficiency. The issue manifested as excessive view... canonical: https://daily.dev/posts/where-did-it-hide-a-swiftui-rendering-bug--c9tvr6fsg twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Where did it hide a SwiftUI rendering bug? | daily.dev og:description: A SwiftUI performance bug went undetected because tests only validated state mutations, not rendering efficiency. The issue manifested as excessive view... og:url: https://daily.dev/posts/where-did-it-hide-a-swiftui-rendering-bug--c9tvr6fsg og:image: https://api.daily.dev/og/posts/c9tVR6fSG.png og:image:alt: Where did it hide a SwiftUI rendering bug? 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. # Where did it hide a SwiftUI rendering bug? **[Rebeloper](https://daily.dev/sources/rebeloper)** · 1 min read · 0 upvotes · 0 comments ## Summary A SwiftUI performance bug went undetected because tests only validated state mutations, not rendering efficiency. The issue manifested as excessive view rebuilds causing CPU spikes on older devices. The solution involved measuring renderer performance and incorporating rendering metrics into the TDD workflow to catch such issues earlier. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: --- Tags: [#performance](https://daily.dev/tags/performance), [#testing](https://daily.dev/tags/testing), [#ios](https://daily.dev/tags/ios), [#swift](https://daily.dev/tags/swift), [#swiftui](https://daily.dev/tags/swiftui) [View this post on daily.dev](https://daily.dev/posts/where-did-it-hide-a-swiftui-rendering-bug--c9tvr6fsg) ```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":"Where did it hide a SwiftUI rendering bug?","url":"https://daily.dev/posts/where-did-it-hide-a-swiftui-rendering-bug--c9tvr6fsg","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/where-did-it-hide-a-swiftui-rendering-bug--c9tvr6fsg"},"datePublished":"2026-01-21T21:51:36.002Z","dateModified":"2026-01-21T21:51:55.623Z","description":"A SwiftUI performance bug went undetected because tests only validated state mutations, not rendering efficiency. 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