private Chain<Searcher> chainedAsSearchChain(Searcher topOfChain) {
        List<Searcher> searchers = new ArrayList<>();
        searchers.add(topOfChain);
        return new Chain<>(searchers);
    }
Helper for testing with a rule base.
Replace subclassing of RuleBaseAbstractTestCase by this.

@author bratseth
container-search/src/test/java/com/yahoo/prelude/semantics/test/RuleBaseTester.java