Incorrect `open-test-report.xml` with parallel test execution

[man85]

Steps to reproduce

Project to reproduce.
Run run-until-fail.sh that will check correctness of open-test-report.xml after running ./gradlew test

Expected correct open-test-report.xml

Context

• JUnit Platform: 5.13.4
• Build Tool: Gradle 8.14.1

Deliverables

Wrong open-test-report.xml:

build/test-results/test/open-test-report.xml:6: parser error : expected '>'

[marcphilipp]

The problem is that you've enabled Gradle's parallel execution (maxParallelForks = 9) feature and all JVMs are now trying to write to the same file (build/test-results/test/open-test-report.xml). As documented in the User Guide, you should configure a separate, unique output directory per forked test JVM using the {uniqueNumber} placeholder. To avoid tracking the absolute path as a task input, a CommandLineArgumentProvider can be used as follows.

tasks.test {
    jvmArgumentProviders += CommandLineArgumentProvider {
        listOf("-Djunit.platform.reporting.output.dir=${reports.junitXml.outputLocation.dir("junit-{uniqueNumber}").get().asFile.absolutePath}")
    }
}

This will result in 9 subdirectories of ``build/test-results/testthat contain anopen-test-report.xml` file each. You can use the Open Test Reporting CLI to generate a single HTML report that includes all of them.