Kotlin suspend function detection doesn't work when JUnit and test method are in a separate ClassLoader

[geoand]

When using JUnit 5 in Quarkus, then tests annotated with @QuarkusTest can't take advantage of the new Kotlin suspend function support.

Although there is needs to be work on Quarkus as well for this to work, currently progress is blocked by JUnit not detecting the suspend methods and instead skipping the test method with a warning like:

2026-02-13 15:24:22,254 WARNING [org.junit.platform.launcher.core.DiscoveryIssueNotifier] (main) TestEngine with ID 'junit-jupiter' encountered a non-critical issue during test discovery:

(1) [WARNING] @Test method 'public final java.lang.Object org.acme.QuarkusSuspendTest.suspendingTestShouldRun(kotlin.coroutines.Continuation<? super kotlin.Unit>)' must not return a value. It will not be executed.
    Source: MethodSource [className = 'org.acme.QuarkusSuspendTest', methodName = 'suspendingTestShouldRun', methodParameterTypes = 'kotlin.coroutines.Continuation']
            at org.acme.QuarkusSuspendTest.suspendingTestShouldRun(SourceFile:0)
[INFO] 

I am using the latest Quarkus version which brings in JUnit 6.0.2

Steps to reproduce

With the following reproducer:

code-with-quarkus.zip

simply execute mvn test

[marcphilipp]

Could you please extract the relevant parts of Quarkus' extension into a standalone extension in the reproducer?

[geoand]

https://github.com/geoand/junit-suspend-classloader-reproducer does not use Quarkus at all, but instead adds only the necessary plumbing for JUnit that effectively does what Quarkus does during testing when it comes to class loading.
This reproducer exhibits the same problem I mentioned in the description.

With #5373, the test is executed as expected

[marcphilipp]

Is there documentation about Quarkus' classloader structure? I would like to know why classes from kotlin-stdlib would be loaded multiple times. Isn't that unnecessary and potentially wasteful?