private void validateThatWeHaveOneGroupLevel() {
        for (StorageGroup group : rootGroup.getSubgroups()) {
            if (group.getSubgroups().size() > 0) {
                throw new IllegalArgumentException("Expected all groups under root group '" +
                                                   rootGroup.getName() + "' to be leaf groups only containing nodes, but sub group '" +
                                                   group.getName() + "' contains " +
                                                   group.getSubgroups().size() + " sub groups");
            }
        }
    }
Class used to validate that hierarchic distribution is correctly setup when having an indexed content cluster.

Note that this class does not implement the com.yahoo.vespa.model.application.validation.Validator interface,
but is instead used in the context of com.yahoo.vespa.model.ConfigProducer.validate() such that it can be unit tested
without having to build the complete vespa model.

@author geirst
config-model/src/main/java/com/yahoo/vespa/model/content/IndexedHierarchicDistributionValidator.java