ArchUnit

Let’s talk architecture today.

ArchUnit is a test framework to test an application architecture.

It is an interesting concept that I wanted to try out for a while. So I did a little experiment on a Swing application I had.

It looks like unit tests with a fluent interface. It’s quite nice to use. I used Junit 5.

My two rules were simple:

• Backend should not use Frontend classes
• Backend should not use Swing or AWT classes

Using ArchUnit, it looks like this (in Kotlin):

@AnalyzeClasses(packages = ["pro.tremblay.myapp.."])
internal class BackendSegregationTest {

    @ArchTest
    val backend_doesnt_use_frontend = layeredArchitecture()
            .layer("backend").definedBy("pro.tremblay.myapp.backend..")
            .layer("frontend").definedBy("pro.tremblay.myapp.frontend..")
            .layer("app").definedBy("pro.tremblay.myapp")
            .whereLayer("frontend").mayOnlyBeAccessedByLayers("app")

    @ArchTest
    val no_ui_framework_on_backend = noClasses().that().resideInAPackage("pro.tremblay.myapp.backend..")
        .should().accessClassesThat().resideInAnyPackage("javax.swing..", "java.awt..");
}

Two simple rules.

• One is defining my layers and how they should interact.
• The other is telling which packages are forbidden.

Sure enough, the test was failing. I did some refactoring to repair everything and ta-da, for ever after, architecture will be enforced.

You might want to try it out on your own project.

I do recommend it.