Martin Kouba I think you may have not deleted the beans.xml that's in src/test/resources/META-INF. When I delete that and just use Priority, tests fail with

groovy.lang.GroovyRuntimeException: Ambiguous method overloading for method java.io.File#<init>

which's because I'm passing null for a file path that the alternative knows how to handle but not the real class. In other words, the alternative doesn't get injected.