ClassCastException when running tests with JUnit 6

[trancexpress]

When running tests, we see the following error:

java.lang.ClassCastException: class org.eclipse.xtext.testing.extensions.InjectionExtension cannot be cast to class org.junit.jupiter.api.extension.Extension (org.eclipse.xtext.testing.extensions.InjectionExtension is in unnamed module of loader org.eclipse.osgi.internal.loader.EquinoxClassLoader @1dbafec0; org.junit.jupiter.api.extension.Extension is in unnamed module of loader org.eclipse.osgi.internal.loader.EquinoxClassLoader @313e7656)
 at java.base/java.util.stream.ForEachOps$ForEachOp$OfRef.accept(ForEachOps.java:186)
 at java.base/java.util.Spliterators$ArraySpliterator.forEachRemaining(Spliterators.java:1024)
 at java.base/java.util.stream.ReferencePipeline$Head.forEach(ReferencePipeline.java:803)
 at java.base/java.util.stream.ReferencePipeline$7$1FlatMap.accept(ReferencePipeline.java:293)
 at java.base/java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:214)
 at java.base/java.util.Collections$2.tryAdvance(Collections.java:5182)
 at java.base/java.util.Collections$2.forEachRemaining(Collections.java:5190)
 at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:570)
 at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:560)
 at java.base/java.util.stream.ForEachOps$ForEachOp.evaluateSequential(ForEachOps.java:153)
 at java.base/java.util.stream.ForEachOps$ForEachOp$OfRef.evaluateSequential(ForEachOps.java:176)
 at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:265)
 at java.base/java.util.stream.ReferencePipeline.forEach(ReferencePipeline.java:632)
 at java.base/java.util.ArrayList.forEach(ArrayList.java:1604)

Should be due to JUnit 5 versions here:

$ cat ./org.eclipse.xtext.testing/META-INF/MANIFEST.MF 
Manifest-Version: 1.0
Bundle-ManifestVersion: 2
Bundle-Name: Xtext Testing Infrastructure
Bundle-SymbolicName: org.eclipse.xtext.testing;singleton:=true
Bundle-Version: 2.41.0.qualifier
Bundle-ClassPath: .
Bundle-Vendor: Eclipse Xtext
...
Import-Package: org.apache.log4j;version="1.2.26",
 org.apache.log4j.spi;version="1.2.26",
 org.junit.jupiter.api;version="[5.1.0,6.0.0)",
 org.junit.jupiter.api.extension;version="[5.1.0,6.0.0)",
 org.junit.jupiter.api.function;version="[5.1.0,6.0.0)",
 org.junit.jupiter.api.io;version="[5.1.0,6.0.0)",
 org.junit.jupiter.params;version="[5.1.0,6.0.0)",
 org.junit.jupiter.params.provider;version="[5.1.0,6.0.0)",
 org.junit.platform.commons.support;version="[1.0.0,2.0.0)";resolution:=optional
...

There are other places that require JUnit 5 too:

$ git grep junit -- "**MANIFEST.MF" | grep "\[5"
org.eclipse.xtext.junit5.tests/META-INF/MANIFEST.MF: org.junit.jupiter.api;version="[5.1.0,6.0.0)",
org.eclipse.xtext.junit5.tests/META-INF/MANIFEST.MF: org.junit.jupiter.api.extension;version="[5.1.0,6.0.0)",
org.eclipse.xtext.junit5.tests/META-INF/MANIFEST.MF: org.junit.jupiter.api.function;version="[5.1.0,6.0.0)",
org.eclipse.xtext.junit5.tests/META-INF/MANIFEST.MF: org.junit.jupiter.api.io;version="[5.1.0,6.0.0)",
org.eclipse.xtext.junit5.tests/META-INF/MANIFEST.MF: org.junit.jupiter.params;version="[5.1.0,6.0.0)",
org.eclipse.xtext.junit5.tests/META-INF/MANIFEST.MF: org.junit.jupiter.params.provider;version="[5.1.0,6.0.0)",
org.eclipse.xtext.testing.junit5.tests/META-INF/MANIFEST.MF: org.junit.jupiter.api;version="[5.1.0,6.0.0)",
org.eclipse.xtext.testing.junit5.tests/META-INF/MANIFEST.MF: org.junit.jupiter.api.extension;version="[5.1.0,6.0.0)",
org.eclipse.xtext.testing.junit5.tests/META-INF/MANIFEST.MF: org.junit.jupiter.api.function;version="[5.1.0,6.0.0)",
org.eclipse.xtext.testing.junit5.tests/META-INF/MANIFEST.MF: org.junit.jupiter.api.io;version="[5.1.0,6.0.0)",
org.eclipse.xtext.testing.junit5.tests/META-INF/MANIFEST.MF: org.junit.jupiter.params;version="[5.1.0,6.0.0)",
org.eclipse.xtext.testing.junit5.tests/META-INF/MANIFEST.MF: org.junit.jupiter.params.provider;version="[5.1.0,6.0.0)",
org.eclipse.xtext.testing/META-INF/MANIFEST.MF: org.junit.jupiter.api;version="[5.1.0,6.0.0)",
org.eclipse.xtext.testing/META-INF/MANIFEST.MF: org.junit.jupiter.api.extension;version="[5.1.0,6.0.0)",
org.eclipse.xtext.testing/META-INF/MANIFEST.MF: org.junit.jupiter.api.function;version="[5.1.0,6.0.0)",
org.eclipse.xtext.testing/META-INF/MANIFEST.MF: org.junit.jupiter.api.io;version="[5.1.0,6.0.0)",
org.eclipse.xtext.testing/META-INF/MANIFEST.MF: org.junit.jupiter.params;version="[5.1.0,6.0.0)",
org.eclipse.xtext.testing/META-INF/MANIFEST.MF: org.junit.jupiter.params.provider;version="[5.1.0,6.0.0)",
org.eclipse.xtext.tests/testdata/wizard-expectations/mavenTychoJUnit5/mavenTychoJUnit5.parent/mavenTychoJUnit5.tests/META-INF/MANIFEST.MF:Import-Package: org.junit.jupiter.api;version="[5.1.0,6.0.0)",
org.eclipse.xtext.tests/testdata/wizard-expectations/mavenTychoJUnit5/mavenTychoJUnit5.parent/mavenTychoJUnit5.tests/META-INF/MANIFEST.MF: org.junit.jupiter.api.extension;version="[5.1.0,6.0.0)"
org.eclipse.xtext.tests/testdata/wizard-expectations/mavenTychoJUnit5/mavenTychoJUnit5.parent/mavenTychoJUnit5.ui.tests/META-INF/MANIFEST.MF:Import-Package: org.junit.jupiter.api;version="[5.1.0,6.0.0)",
org.eclipse.xtext.tests/testdata/wizard-expectations/mavenTychoJUnit5/mavenTychoJUnit5.parent/mavenTychoJUnit5.ui.tests/META-INF/MANIFEST.MF: org.junit.jupiter.api.extension;version="[5.1.0,6.0.0)"
org.eclipse.xtext.ui.testing/META-INF/MANIFEST.MF: org.junit.jupiter.api;version="[5.0.0,6.0.0)";resolution:=optional,

How do we want to deal with that? Drop JUnit 5 support and move the dependencies to JUnit 6?

[cdietrich]

@trancexpress i dont really have time to look into that
nor to work on that
if so it would be a topic for 2026-03 anyway due to release next week.

• can you give a comprehensive list of changes in junit6
• do you think there is a way to support both versions?

e.g. widening the range and have a org.eclipse.xtext.testing.extensions.InjectionExtension
or is there a way to execute junit5 tests with junit 6

[cdietrich]

@szarnekow @LorenzoBettini what is your take?

[cdietrich]

cc @SimonCockx how did you deal with that problem (following https://github.com/eclipse-xtext/xtext/pull/3541/files)

[trancexpress]

can you give a comprehensive list of changes in junit6

https://docs.junit.org/6.0.0-M1/release-notes/

Nothing of importance for Xtext, I think, at most this one:

Require Java 17 

I assume this is the reason for a new major release, all the APIs are not changed.

do you think there is a way to support both versions?

I am sure there is, JDT and PDE both do. I don't think its worth the trouble though, for Xtext.

e.g. widening the range and have a org.eclipse.xtext.testing.extensions.InjectionExtension

I don't know if that will work. Mixing JUnit 5 and JUnit 6 leads to all kinds of problems. Maybe if widening the range never leads to adding JUnit 5, when launching tests with JUnit 6 and the other way around...

or is there a way to execute junit5 tests with junit 6

Sure, API-wise there are no differences. The problem in this issue comes from Xtext depending on JUnit 5 bundles, but we are running on JUnit 6.

I don't know how support for both versions would work. In JDT we copied everything from org.eclipse.jdt.junit5.runtime to a enw bundle org.eclipse.jdt.junit6.runtime.

[SimonCockx]

@cdietrich I didn't encounter this problem. Perhaps because I'm using the junit bom, so there was no inconsistency between versions?

[iloveeclipse]

can you give a comprehensive list of changes in junit6

https://docs.junit.org/6.0.0-M1/release-notes/

https://docs.junit.org/6.0.0/release-notes/

[LorenzoBettini]

@szarnekow @LorenzoBettini what is your take?

Maybe widening the range so that we verify whether we don't have problems with JUnit 6.

However, since we have those ranges, why is JUnit 6 being used and not excluded?

[trancexpress]

However, since we have those ranges, why is JUnit 6 being used and not excluded?

We are moving our tests to run on JUnit 6. Our test bundles load JUnit 6, the org.eclipse.xtext.testing loads JUnit 5. The conflict results in the CCE.

[trancexpress]

Workaround for us was to copy InjectionExtension.