Problem with Maven-Tycho build in GitLab CI


We are building an Eclipse Xtext based project with Maven and the Tycho plugin. Everything works fine, except for the automated tests in GitLab CI/CD. These fail because somehow the main class in the org.eclipse.equinox.launcher dependency cannot be found:

148908 [INFO] Command line:
[/usr/lib/jvm/java-11-openjdk-amd64/bin/java, -Dosgi.noShutdown=false, -Dosgi.os=linux,, -Dosgi.arch=x86_64, , --add-modules=ALL-SYSTEM, -Dosgi.clean=true, -jar, /builds/qrml/qrml-dsl/.m2/repository/p2/osgi/bundle/org.eclipse.equinox.launcher/1.5.700.v20200207-2156/org.eclipse.equinox.launcher-1.5.700.v20200207-2156.jar, -debug, -consolelog, -data, /builds/qrml/qrml-dsl/QRML_tooling/qrml-2.0/, -install, /builds/qrml/qrml-dsl/QRML_tooling/qrml-2.0/, -configuration, /builds/qrml/qrml-dsl/QRML_tooling/qrml-2.0/, -application, org.eclipse.tycho.surefire.osgibooter.headlesstest, -testproperties, /builds/qrml/qrml-dsl/QRML_tooling/qrml-2.0/]
Error: Could not find or load main class
Caused by: java.lang.ClassNotFoundException:

Locally (windows environment) this works fine: tests are executed normally as expected during the Maven build. I tried to add the org.eclipse.equinox.launcher explicitly (test scope) but that doesn’t help. Juding from the log files, the jar is present.

Any hints or pointers on how to solve this are greatly appreciated, thanks!

Best regards,