JDK 11 + JUnit 5 + Jigsaw: Junit fails to run tests for `module-info` - gradle

Question

I try to use JUnit 5 in a Gradle project. compileJava and compileTestJava both succeed, but test fails with the strange message Could not execute test class 'module-info'. (message from stacktrace):
> Task :test FAILED
FAILURE: Build failed with an exception.
* What went wrong:
Execution failed for task ':test'.
> There were failing tests. See the report at: file:///Users/axel/git/utility/build/reports/tests/test/index.html
The test result file hints me that "failed to execute tests", but the stack trace looks weird. It seems JUnit is trying to run the class corresponding to my module-info.java file:
org.gradle.api.internal.tasks.testing.TestSuiteExecutionException: Could not execute test class 'module-info'.
at org.gradle.api.internal.tasks.testing.SuiteTestClassProcessor.processTestClass(SuiteTestClassProcessor.java:53)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:566)
at org.gradle.internal.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:35)
at org.gradle.internal.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:24)
at org.gradle.internal.dispatch.ContextClassLoaderDispatch.dispatch(ContextClassLoaderDispatch.java:32)
at org.gradle.internal.dispatch.ProxyDispatchAdapter$DispatchingInvocationHandler.invoke(ProxyDispatchAdapter.java:93)
at com.sun.proxy.$Proxy2.processTestClass(Unknown Source)
at org.gradle.api.internal.tasks.testing.worker.TestWorker.processTestClass(TestWorker.java:117)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:566)
at org.gradle.internal.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:35)
at org.gradle.internal.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:24)
at org.gradle.internal.remote.internal.hub.MessageHubBackedObjectConnection$DispatchWrapper.dispatch(MessageHubBackedObjectConnection.java:155)
at org.gradle.internal.remote.internal.hub.MessageHubBackedObjectConnection$DispatchWrapper.dispatch(MessageHubBackedObjectConnection.java:137)
at org.gradle.internal.remote.internal.hub.MessageHub$Handler.run(MessageHub.java:404)
at org.gradle.internal.concurrent.ExecutorPolicy$CatchAndRecordFailures.onExecute(ExecutorPolicy.java:63)
at org.gradle.internal.concurrent.ManagedExecutorImpl$1.run(ManagedExecutorImpl.java:46)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
at org.gradle.internal.concurrent.ThreadFactoryImpl$ManagedThreadRunnable.run(ThreadFactoryImpl.java:55)
at java.base/java.lang.Thread.run(Thread.java:834)
Caused by: java.lang.NoClassDefFoundError: module-info is not a class because access_flag ACC_MODULE is set
at java.base/java.lang.ClassLoader.defineClass1(Native Method)
at java.base/java.lang.ClassLoader.defineClass(ClassLoader.java:1016)
at java.base/java.security.SecureClassLoader.defineClass(SecureClassLoader.java:174)
at java.base/jdk.internal.loader.BuiltinClassLoader.defineClass(BuiltinClassLoader.java:801)
at java.base/jdk.internal.loader.BuiltinClassLoader.findClassOnClassPathOrNull(BuiltinClassLoader.java:699)
at java.base/jdk.internal.loader.BuiltinClassLoader.loadClassOrNull(BuiltinClassLoader.java:622)
at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:580)
at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:178)
at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:521)
at java.base/java.lang.Class.forName0(Native Method)
at java.base/java.lang.Class.forName(Class.java:398)
at org.gradle.api.internal.tasks.testing.junitplatform.JUnitPlatformTestClassProcessor.loadClass(JUnitPlatformTestClassProcessor.java:103)
at org.gradle.api.internal.tasks.testing.junitplatform.JUnitPlatformTestClassProcessor.access$200(JUnitPlatformTestClassProcessor.java:54)
at org.gradle.api.internal.tasks.testing.junitplatform.JUnitPlatformTestClassProcessor$CollectAllTestClassesExecutor.execute(JUnitPlatformTestClassProcessor.java:82)
at org.gradle.api.internal.tasks.testing.junitplatform.JUnitPlatformTestClassProcessor$CollectAllTestClassesExecutor.execute(JUnitPlatformTestClassProcessor.java:77)
at org.gradle.api.internal.tasks.testing.junit.AbstractJUnitTestClassProcessor.processTestClass(AbstractJUnitTestClassProcessor.java:66)
at org.gradle.api.internal.tasks.testing.SuiteTestClassProcessor.processTestClass(SuiteTestClassProcessor.java:51)
... 25 more
versions used:
jin:utility axel$ java -version
openjdk version "11" 2018-09-25
OpenJDK Runtime Environment 18.9 (build 11+28)
OpenJDK 64-Bit Server VM 18.9 (build 11+28, mixed mode)
jin:utility axel$ ./gradlew -version
WARNING: An illegal reflective access operation has occurred
WARNING: Illegal reflective access by org.codehaus.groovy.reflection.CachedClass (file:/Users/axel/.gradle/wrapper/dists/gradle-4.10.2-bin/cghg6c4gf4vkiutgsab8yrnwv/gradle-4.10.2/lib/groovy-all-2.4.15.jar) to method java.lang.Object.finalize()
WARNING: Please consider reporting this to the maintainers of org.codehaus.groovy.reflection.CachedClass
WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations
WARNING: All illegal access operations will be denied in a future release
------------------------------------------------------------
Gradle 4.10.2
------------------------------------------------------------
Build time: 2018-09-19 18:10:15 UTC
Revision: b4d8d5d170bb4ba516e88d7fe5647e2323d791dd
Kotlin DSL: 1.0-rc-6
Kotlin: 1.2.61
Groovy: 2.4.15
Ant: Apache Ant(TM) version 1.9.11 compiled on March 23 2018
JVM: 11 (Oracle Corporation 11+28)
OS: Mac OS X 10.14 x86_64
jin:utility axel$ grep -i junit build.gradle
// JUnit
testImplementation 'org.junit.jupiter:junit-jupiter-api:5.3.1'
testRuntimeOnly 'org.junit.jupiter:junit-jupiter-engine:5.3.1'
useJUnitPlatform()
Does anyone know how to tell JUnit not to try to run module-info or any other workaround?

Answer 1

Ignoring module-info.class at test-runtime is "Resort to the class-path": https://sormuras.github.io/blog/2018-09-11-testing-in-the-modular-world#resort-to-the-classpath -- your tests may access internal classes as before. All modular boundaries are discarded.
If you want stay in the modular world when doing white box tests, you need to patch your main and test modules into a single one. Either at test compile or test runtime. More information about that test modes can also be found in the blog linked above.
For a Gradle setup you may either use the JUnit ConsoleLauncher manually or re-configure the Gradle runtime paths like described here https://guides.gradle.org/building-java-9-modules/ and/or use https://github.com/zyxist/chainsaw

Answer 2

Works if I add a filter in build.gradle:
test {
useJUnitPlatform()
filter {
exclude '**/module-info.class'
}
}