private static void requireFixedSizeSingularNodeIfTester(ConfigModelContext context, NodesSpecification nodes) {
        if ( ! context.properties().hostedVespa() || ! context.properties().applicationId().instance().isTester())
            return;

        if ( ! nodes.maxResources().equals(nodes.minResources()))
            throw new IllegalArgumentException("tester resources must be absolute, but min and max resources differ: " + nodes);

        if (nodes.maxResources().nodes() > 1)
            throw new IllegalArgumentException("tester cannot run on more than 1 node, but " + nodes.maxResources().nodes() + " nodes were specified");
    }
Allocate a container cluster without a nodes tag
config-model/src/main/java/com/yahoo/vespa/model/container/xml/ContainerModelBuilder.java