### Question:
SolrCriterionTransformer { public String join(List<String> criteria) { if (CollectionUtils.isEmpty(criteria)) { return StringUtils.EMPTY; } return criteria.stream().collect(Collectors.joining(" ")); }  String transformToEqualsCriterionWithParsing(F field, String value); String transformToEqualsCriterion(F field, String value); String transformToEqualsCriterion(F field, String value, Operator operator); String transformToEqualsCriterion(F field, Integer value); String transformToEqualsCriterion(F field, Long value); String transformToEqualsCriterion(F field, Enum<?> enumValue); String transformToEqualsCriteria(F field, List<String> values, Operator operator); String transformToEqualsEnumCriteria(F field, List<? extends Enum<?>> values, Operator operator); String transformToDateRangeCriterion(F field, LocalDate from, LocalDate to); String transformToRangeCriterion(F field, String from, String to); String and(String criterion); String join(List<String> criteria);  }### Answer:
@Test public void join() { String actual = criterionTransformer.join(Lists.newArrayList("aa:bb","+cc:dd")); assertEquals("aa:bb +cc:dd", actual); }