--- title: Day 22/30 — Test Behaviour | daily.dev description: A short testing philosophy piece for NestJS applications, arguing that tests should validate application behavior rather than implementation details like... canonical: https://daily.dev/posts/day-22-30-test-behaviour-d5kdwtggz twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Day 22/30 — Test Behaviour | daily.dev og:description: A short testing philosophy piece for NestJS applications, arguing that tests should validate application behavior rather than implementation details like... og:url: https://daily.dev/posts/day-22-30-test-behaviour-d5kdwtggz og:image: https://api.daily.dev/og/posts/D5kdwtGGz.png og:image:alt: Day 22/30 — Test Behaviour 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. # Day 22/30 — Test Behaviour **[Nestjs Developers](https://daily.dev/sources/nestjsdevs)** · [@ezilemdodana](https://daily.dev/ezilemdodana) · 1 min read · 12 upvotes · 2 comments ## Summary A short testing philosophy piece for NestJS applications, arguing that tests should validate application behavior rather than implementation details like decorators. It outlines a practical layering strategy: unit tests for business logic, integration tests for infrastructure boundaries, and end-to-end tests for critical user journeys, with a call to pick the smallest test that catches the failure you care about. ## Content Test what your application does, not how many decorators the class contains. A practical NestJS testing approach: - Unit tests for business decisions - Integration tests for infrastructure boundaries - End-to-end tests for critical user journeys If every dependency is mocked, your tests may only prove that the mocks agree with each other. If every test boots the whole application, feedback becomes slow and fragile. Choose the smallest test capable of catching the failure you care about. Which testing layer gives your project the most confidence? #NestJS #Testing #SoftwareQuality ## Community discussion Top comments from developers on daily.dev. **@navyaak** · 1 upvotes > Developer testing **@agustinbarrientos** · 0 upvotes > At service boundaries, I'd keep contract tests. They catch integration drift without paying the startup cost of a full end-to-end suite. ## Similar posts on daily.dev - [Module Test](https://daily.dev/posts/module-test-7cztbz9zp) · The Daily WTF · 1 upvotes · 1 comments - [An advanced guide to Nuxt testing and mocking](https://daily.dev/posts/an-advanced-guide-to-nuxt-testing-and-mocking-qzstakmm0) · LogRocket · 1 upvotes · 0 comments - [How Cloud-Native Complexity is Outpacing Test Automation Strategy](https://daily.dev/posts/how-cloud-native-complexity-is-outpacing-test-automation-strategy-aizwf7ic6) · Cloud Native Now · 0 upvotes · 0 comments - [TDD is a Luxury: Pragmatic Testing for the Solo Developer](https://daily.dev/posts/tdd-is-a-luxury-pragmatic-testing-for-the-solo-developer-tawfchoo4) · Ruby Flow · 0 upvotes · 1 comments - [Stop Writing Database-Dependent Tests — Mock Your Data Access Layer](https://daily.dev/posts/stop-writing-database-dependent-tests-mock-your-data-access-layer-quo7rycbz) · Javarevisited · 98 upvotes · 10 comments --- Tags: [#testing](https://daily.dev/tags/testing), [#typescript](https://daily.dev/tags/typescript), [#nestjs](https://daily.dev/tags/nestjs) [View this post on daily.dev](https://daily.dev/posts/day-22-30-test-behaviour-d5kdwtggz) ```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":"DiscussionForumPosting","mainEntityOfPage":"https://daily.dev/posts/day-22-30-test-behaviour-d5kdwtggz","headline":"Day 22/30 — Test Behaviour","text":"A short testing philosophy piece for NestJS applications, arguing that tests should validate application behavior rather than implementation details like decorators. 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