Not able to write junit test case for jpa specification

Question

I have a PersonServiceImpl class in which I am fetching record from repository like this.

personRepo.findAll(**new Specification<Person>**() {
                @Override
                public Predicate toPredicate(Root<Person> root, CriteriaQuery<?> query,        Criteria Builder cb) {

                }
              }, pageable);

I am trying to cover this whole predicate method using JUnit but not able to do this. It's only covering all codes except inner part of find All.

I have spent much time over internet but didn't find any solution. Please help.