How to ignore classes in test class with ArchUnit

In case you are not using archunit-junit (ArchUnit's JUnit4-support as time of writing), but using "native" ArchUnit, use (for example)

com.tngtech.archunit.core.domain.JavaClasses classes 
  = new com.tngtech.archunit.core.importer.ClassFileImporter()
    .withImportOption(
      new com.tngtech.archunit.core.importer.ImportOption.DoNotIncludeTests())
    .importPackages("my.random.package");

It seems that the API is not guiding very well with respect to this, because you're not the first one wondering about this (this was also issue #1 on Github https://github.com/TNG/ArchUnit/issues/1).

To answer the question though, the Annotation @AnalyseClasses has an extra attribute importOptions, which takes arbitrary implementations of ImportOption. There you can specify which Location (basically the URI) to include.

Since excluding tests is rather common, this ImportOption is already predefined (for Maven and Gradle < 4.0), so you can write

@AnalyzeClasses(..., importOptions = ImportOption.DoNotIncludeTests.class)
public class MyTest{ ... }

I don't think, there is a generic solution for all setups (thus the freedom to just write your own ImportOption to decide which locations to include). However, for standard Maven and Gradle setups, it should be working.