public Subject insertSubject(String apiKey, String subjectName) {
        return subjectRepository.save(makeSubject(apiKey, subjectName));
    }
Current method assumes, that model with such api_key already exists

@param apiKey      existing api key (app and model already in DB)
@param subjectName subject name
@return subject object
java/api/src/test/java/com/exadel/frs/core/trainservice/DbHelper.java