Support JUnit Platform 6.0.x (unified versioning from JUnit 6)

[clara-deadline]

Problem

JUnit 6.0.0 shipped with unified versioning — all artifacts (Platform, Jupiter, Vintage) now share the same 6.0.x version number. What was previously junit-platform-engine:1.10.x is now junit-platform-engine:6.0.x.

Spring Boot 4.0.5 ships JUnit Platform 6.0.3 by default. Projects on Spring Boot 4 cannot use the pitest-junit5-plugin because the plugin's coverage analysis phase finds 0% coverage and runs 0 tests per mutation.

Reproduction

Environment:

• JDK 25 (Temurin 25.0.2+10)
• Gradle 8.14
• Spring Boot 4.0.5
• junit-platform-engine:6.0.3 (managed by Spring Boot BOM)
• gradle-pitest-plugin:1.15.0 (1.19.0 corrupts the test classpath — see below)
• pitest:1.22.1 (for JDK 25 / ASM 9.8+ support)
• pitest-junit5-plugin:1.2.1 and 1.2.2 (both tested)

Config (Gradle Kotlin DSL):

pitest {
    pitestVersion.set("1.22.1")
    junit5PluginVersion.set("1.2.2")
    targetClasses.set(setOf("com.example.*"))
    mutationThreshold.set(60)
}

Result:

8:41:22 PIT >> INFO : Sending 362 test classes to minion
>> Line Coverage (for mutated classes only): 0/3298 (0%)
>> Generated 1132 mutations Killed 0 (0%)
>> Mutations with no coverage 1132. Test strength 100%
>> Ran 0 tests (0 tests per mutation)

PIT discovers the test classes (362) and generates mutations (1132), but the coverage analysis phase cannot execute any tests — presumably because the shaded JUnit Platform classes inside the plugin are version 1.x and don't match the 6.x runtime.

Additional observation: gradle-pitest-plugin:1.19.0 causes a separate issue — it corrupts the Gradle test classpath so that even non-Pitest gradle test tasks fail with "Could not complete execution for Gradle Test Executor". Reverting to 1.15.0 restores normal test execution (but the 0-coverage Pitest issue remains).

Expected behavior

The pitest-junit5-plugin should work with JUnit Platform 6.0.x, since JUnit 6 is described as a smooth migration from JUnit 5 with unchanged annotations, extensions, and test discovery API.

Likely fix

Since JUnit 6 is API-compatible with JUnit 5 (unified versioning, not a rewrite), the fix is likely:

1. Bump the shaded junit-platform-launcher dependency to 6.0.x
2. Update version compatibility checks that may be gating on 1.x platform versions
3. Re-shade and release

Impact

This blocks mutation testing for any project on Spring Boot 4+ (which is the current GA release). Spring Boot 4 manages junit-platform:6.0.3 via its BOM, and there's no clean way to downgrade to Platform 1.x without breaking Spring's test infrastructure.

References

• JUnit 6.0.3 Release Notes
• Upgrading to JUnit 6.0 (wiki)
• JUnit Platform 6.0.0 on Maven Central

[hcoles]

@clara-deadline

Can you please supply a minimal example project that reproduces the issue.