private Optional<DocumentFrequency> getModelDocumentFrequencyWithEnglish(String word) {
        SignificanceModel model = significanceModelRegistry.getModel(Language.ENGLISH).get();
        return makeDocumentFrequency(model.documentFrequency(word));
    }
Tests significance term in the search chain.

@author MariusArhaug
container-search/src/test/java/com/yahoo/search/significance/test/SignificanceSearcherTest.java