ArchUnit practice: Enforce package private visibility of classes that depend only on the same package

//Execution environment
* AdoptOpenJDK 11.0.9.1+1
* JUnit 5.7.0
* ArchUnit 0.14.1

Architectural test motivation

• I want to hide the concerns closed inside the package from outside the package
• I want to prevent unexpected dependencies (combinations) from outside the package at the language specification level.
• I want to improve maintainability (easiness of understanding and change) by limiting the scope of disclosure.

Architecture test implementation

package com.example;
　
import com.tngtech.archunit.base.DescribedPredicate;
import com.tngtech.archunit.core.domain.Dependency;
import com.tngtech.archunit.core.domain.JavaClass;
import com.tngtech.archunit.core.domain.JavaClasses;
import com.tngtech.archunit.core.importer.ClassFileImporter;
import com.tngtech.archunit.core.importer.ImportOption;
import org.junit.jupiter.api.Test;

import static com.tngtech.archunit.lang.syntax.ArchRuleDefinition.classes;

class ArchitectureTest {

    //Class to be inspected
    private static final JavaClasses CLASSES =
            new ClassFileImporter()
                    .withImportOption(ImportOption.Predefined.DO_NOT_INCLUDE_TESTS)
                    .importPackages("com.example");

    @Test
void Make classes that depend only from the same package package private() {
        classes()
            .that()
            .arePublic()
            .and(new DescribedPredicate<>("only have dependent classes that reside in same package") {
                @Override
                public boolean apply(final JavaClass clazz) {
                    return clazz.getDirectDependenciesToSelf()
                        .stream()
                        .map(Dependency::getOriginClass)
                        .allMatch(dependentClass
                            -> dependentClass.getPackageName().equals(clazz.getPackageName()));
                }
            })
            .should()
            .notBePublic()
            .check(CLASSES);
    }
}