tng/archunit

ArchUnit is a Java library that lets you write automated tests for your code's architecture. In software projects, architecture refers to rules about how code is organized: which parts of the codebase are allowed to talk to each other, how layers are separated, whether there are circular dependencies, and so on. Without a tool like this, those rules typically live only in documentation or team memory and violations accumulate silently over time. ArchUnit lets you express the rules as regular unit tests that run in your existing test suite. The library works by scanning your compiled Java bytecode, loading all the classes into an in-memory structure, and then checking them against rules you define in Java code. The rules are written using a fluent API that reads roughly like English: you state that certain classes should only depend on certain other classes, that packages should follow a specific layering pattern, or that there should be no cyclic dependencies between a given set of packages. If any class violates a rule, the test fails and reports exactly which violation occurred. Adding ArchUnit to a project takes two steps: add it as a test dependency via Maven or Gradle, then write a test class with one or more rule checks. The library integrates with standard Java test frameworks like JUnit, so no special tooling is required beyond what most Java projects already have. Common use cases include enforcing a layered architecture (controllers only call services, services only call repositories, repositories only touch the database), preventing circular package dependencies, and ensuring naming conventions are followed across a codebase. The library is free, open-source, and published under the Apache License 2.0.