Gradle regression in tests when a module has a "sidecar" module

[celcius112]

Describe the bug

From Quarkus 3.22.0 to Quarkus 3.23.0 there is a regression in @QuarkusTest when a module A uses a class from module B that reference a class from module A. In this situation, a ClassNotFoundException is thrown. There is no problem in Quarkus 3.21.4.

Let's say module A has a class Person:

public record Person(String id) {}

And module B a PersonFactory:

public class PersonFactory {
	public static Person newRandomPerson() {
		return new Person(UUID.randomUUID().toString());
	}
}

module A imports B as a test dependency:

dependencies {
    ...
    testImplementation(project(":B"))
    testImplementation("io.quarkus:quarkus-junit5")
}

And module B imports A as a main dependency:

dependencies {
    implementation(project(":A"))
}

If module A uses PersonFactory#newRandomPerson in a @QuarkusTest, a ClassNotFoundException is thrown:

@QuarkusTest
class PersonTest {
	@Test
	void test() {
		PersonFactory.newRandomPerson();
	}
}

With the stacktrace being:

java.lang.NoClassDefFoundError: com/module/Person
	at com.module.test.PersonFactory.newRandomPerson(PersonFactory.java:9)
	at com.module.PersonTest.test(PersonTest.java:12)
	at java.base/java.lang.reflect.Method.invoke(Method.java:580)
	at io.quarkus.test.junit.QuarkusTestExtension.runExtensionMethod(QuarkusTestExtension.java:999)
	at io.quarkus.test.junit.QuarkusTestExtension.interceptTestMethod(QuarkusTestExtension.java:847)
	at java.base/java.util.ArrayList.forEach(ArrayList.java:1596)
	at java.base/java.util.ArrayList.forEach(ArrayList.java:1596)
Caused by: java.lang.ClassNotFoundException: com.module.Person
	at io.quarkus.bootstrap.classloading.QuarkusClassLoader.loadClass(QuarkusClassLoader.java:549)
	at io.quarkus.bootstrap.classloading.QuarkusClassLoader.loadClass(QuarkusClassLoader.java:523)
	... 7 more

How to Reproduce?

Here's a reproducer:
test-classloader-issue.zip

1. Go to PersonFactory and launch the test
   • A ClassNotFoundException should be thrown
2. In gradle.properties use the Quarkus version 3.21.4
3. Run the test again
   • The test should pass

Output of uname -a or ver

Darwin MacBook-Pro.local 24.5.0 Darwin Kernel Version 24.5.0: Tue Apr 22 19:53:27 PDT 2025; root:xnu-11417.121.6~2/RELEASE_ARM64_T6041 arm64

Output of java -version

openjdk version "21.0.5" 2024-10-15 LTS OpenJDK Runtime Environment Temurin-21.0.5+11 (build 21.0.5+11-LTS) OpenJDK 64-Bit Server VM Temurin-21.0.5+11 (build 21.0.5+11-LTS, mixed mode, sharing)

Quarkus version or git rev

3.22.0 to 3.23.0

Build tool (ie. output of mvnw --version or gradlew --version)

Gradle 8.13 and 8.14

Additional information

May be related to #48157, but I am not sure.

[quarkus-bot]

/cc @geoand (kotlin), @glefloch, @quarkusio/devtools

[geoand]

cc @aloubyansky @holly-cummins

[Chu3laMan]

@celcius112

I tried your project that simulates the issue, the main issue is coming from the following line

ClassPathElement classPathElement = classPathResourceIndex.getFirstClassPathElement(resourceName);

which is load all available JAR, Module, and Directories

means, PersonFactory tries to access the Person which is expected to be found, on the actual issue is seems does not exist

[reaver585]

I was looking into this issue now, on latest master. From what I can see, PersonTest and PersonFactory are loaded using Quarkus Runtime ClassLoader, whereas loading of Person class from the factory class happens via Quarkus Base Runtime ClassLoader, and that loader throws here:

if (classPathResourceIndex.isBanned(resourceName)) {
    throw new ClassNotFoundException(name);
}

Person class is banned in the base runtime classloader since it's marked as reloadable.

I will continue looking into it and try to understand what changed from 3.22.0 to 3.23.0 that caused this. I'm not an expert in this topic, so most likely I might need to validate it with more experienced folks in Zulip, and it may take a bit of time. You should get an update soon, @celcius112 .