--- title: My test suite was green and the extension was broken for... description: A developer shipped a Chrome extension where all tests passed but the extension was broken for every real user. The root cause: content scripts declared in the... canonical: https://daily.dev/posts/my-test-suite-was-green-and-the-extension-was-broken-for-every-single-person-who-installed-it-lta1agwd5 twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: My test suite was green and the extension was broken for every single person who installed it | daily.dev og:description: A developer shipped a Chrome extension where all tests passed but the extension was broken for every real user. The root cause: content scripts declared in the... og:url: https://daily.dev/posts/my-test-suite-was-green-and-the-extension-was-broken-for-every-single-person-who-installed-it-lta1agwd5 og:image: https://api.daily.dev/og/posts/LtA1AGwd5.png og:image:alt: My test suite was green and the extension was broken for every single person who installed it 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. # My test suite was green and the extension was broken for every single person who installed it **[Medium](https://daily.dev/sources/medium_js)** · 5 min read · 0 upvotes · 0 comments ## Summary A developer shipped a Chrome extension where all tests passed but the extension was broken for every real user. The root cause: content scripts declared in the manifest only attach to pages loaded after the extension installs, meaning all pre-existing tabs are inert. The test suite always loaded the extension before opening pages — the exact opposite of real user behavior — making the bug structurally impossible to catch. The fix involved using the scripting API to inject the content script into all open tabs on install/update. The key lesson: ask not 'what am I not testing' but 'what does my test setup make impossible?' ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Similar posts on daily.dev - [How I Built a Chrome Extension Wrapper \(and Everything That Tried to Stop Me\)](https://daily.dev/posts/how-i-built-a-chrome-extension-wrapper-and-everything-that-tried-to-stop-me--zn0uywaqq) · thoughbot · 1 upvotes · 0 comments - [I Shipped My First Chrome Extension](https://daily.dev/posts/i-shipped-my-first-chrome-extension-kqiqfemcp) · Alex CloudStar · 1 upvotes · 1 comments - [Taming Agentic Browsers: Vulnerability in Chrome Allowed Extensions to Hijack New Gemini Panel](https://daily.dev/posts/taming-agentic-browsers-vulnerability-in-chrome-allowed-extensions-to-hijack-new-gemini-panel-wrgfp6s8g) · Unit 42 · 0 upvotes · 0 comments - [Make a Chrome Extension to Digest Webpages with Manifest V3 and Groq API](https://daily.dev/posts/make-a-chrome-extension-to-digest-webpages-with-manifest-v3-and-groq-api-ve1j1mfbv) · PyImageSearch · 0 upvotes · 0 comments --- Tags: [#devtools](https://daily.dev/tags/devtools), [#testing](https://daily.dev/tags/testing) [View this post on daily.dev](https://daily.dev/posts/my-test-suite-was-green-and-the-extension-was-broken-for-every-single-person-who-installed-it-lta1agwd5) ```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":"My test suite was green and the extension was broken for every single person who installed it","url":"https://daily.dev/posts/my-test-suite-was-green-and-the-extension-was-broken-for-every-single-person-who-installed-it-lta1agwd5","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/my-test-suite-was-green-and-the-extension-was-broken-for-every-single-person-who-installed-it-lta1agwd5"},"datePublished":"2026-07-17T18:24:27.571Z","dateModified":"2026-07-17T18:26:04.763Z","description":"A developer shipped a Chrome extension where all tests passed but the extension was broken for every real user. 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