Create unit test to package Service

[OlhenShu]

Create unit test to GreenCityMVP service/src/main/java/greencity/service

1. • [ ] HabitAssignServiceImpl
2. • [ ] HabitFactServiceImpl
3. • [ ] HabitServiceImpl
4. • [ ] HabitShoppingListItemServiceImpl
5. • [ ] HabitStatisticServiceImpl
6. • [ ] HabitStatusCalendarServiceImpl
7. • [ ] LanguageServiceImpl
8. • [ ] ManagementHabitServiceImpl
9. • [ ] RatingStatisticsServiceImpl
10. • [ ] SearchServiceImpl
11. • [ ] ShoppingListItemServiceImpl
12. • [ ] SpecificationServiceImpl

Acceptance Criteria:

• All tests pass successfully.
• The code is clean and adheres to coding standards.
• Dependencies are correctly mocked, and their methods are verified for calls.
• Test coverage should be 100%.