private void checkSubstrings(String[] fields, String haystack, int offset) {
        for (String field : fields) {
            assertTrue(-1 < haystack.indexOf(field, offset));
        }
    }
Tests the JSONString XML rendering.

TODO: Add correct answers. These are not added because this code was checked in before sync with system test

@author Steinar Knutsen
container-search/src/test/java/com/yahoo/prelude/hitfield/test/JSONStringTestCase.java