Hi I need help to test this program using junit 4 please test all methods and do not leave anything out show me the output once you have tested thank you.

package medical.com.medicalApplication.services;

import java.util.ArrayList; import java.util.List;

import medical.com.medicalApplication.model.Doctor; /** * * This class uses a singleton pattern to mock a service instead of using dependency injection * * In addition, it stores data in memory only using Lists * */ public class DoctorService { private static DoctorService reference = new DoctorService(); private static List doctors; DoctorService(){ doctors = new ArrayList(); } public static DoctorService getReference(){ return reference; } public List getAllDoctors(){ return doctors; } public boolean addDoctor(String name, String id){ String tempId = new String(id); boolean createDoctor = !doctors.stream().anyMatch(doctor -> doctor.getId() == tempId); if (createDoctor) { doctors.add(new Doctor(name, id)); } return createDoctor; }

}