the first part

src/StudentTest.java

+import com.university.Department;
+import com.university.Student;
+import org.junit.Before;
+import org.junit.BeforeClass;
+import org.junit.Test;
+import org.junit.jupiter.api.BeforeAll;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotNull;
+
+
+public class StudentTest {
+    static Student student;
+    static Department department;
+
+    @BeforeAll
+    public static void createStudent(){
+        department = new Department("Computer and IT Eng");
+        student = new Student("Alireza", "1234", "Software Eng", department);
+    }
+
+    @Test
+    public void testStudentGetName(){
+
+        assertEquals("Alireza", student.getName());
+    }
+
+    @Test
+    public void testStudenGetCourses(){
+        assertNotNull(student.getCourses());
+        assertEquals(0, student.getCourses().length);
+    }
+
+}

src/com/university/Course.java

+package com.university;
+
+import java.util.ArrayList;
+
+public class Course {
+    private String ID;
+    private String name;
+    private Department dpart;
+    private Professor prof;
+    private int credit;
+    private ArrayList<Student> stds = new ArrayList<Student>();
+
+    public Course(String ID, String name, Department department, Professor professor, int credit) {
+        this.ID = ID;
+        this.name = name;
+        dpart = department;
+        prof = professor;
+        this.credit = credit;
+    }
+
+    public String getID(){
+        return ID;
+    }
+
+    public Department getDepartment(){
+        return dpart;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public Student[] getStudents() {
+        Student[] students = stds.toArray(new Student[stds.size()]);
+        return students;
+    }
+
+    public Professor getProfessor() {
+        return prof;
+    }
+
+    public int getCredit() {
+        return credit;
+    }
+
+    public void enrollStudent(Student student){
+        stds.add(student);
+
+    }
+
+}

src/com/university/Department.java

+package com.university;
+
+public class Department {
+    private String name;
+    public Department(String name) {
+        this.name = name;
+    }
+
+    public String getName(){
+        return name;
+    }
+
+    public void addStudent(Student student){
+
+    }
+
+    public Student[] getStudents(){
+        return null;
+    }
+
+    public void removeStudent(Student student){
+
+    }
+
+    public void addCourse(Course course){
+
+    }
+
+    public Course[] getCourses(){
+        return null;
+    }
+
+    public void removeCourse(Course course){
+
+    }
+
+    public void addProfessor(Professor student){
+
+    }
+
+    public Professor[] getProfessors(){
+        return null;
+    }
+
+    public void removeProfessor(Professor professor){
+
+    }
+
+}

src/com/university/Professor.java

+package com.university;
+
+import java.util.ArrayList;
+
+public class Professor {
+    private String name;
+    private Department dpart;
+    private ArrayList<Course> crs = new ArrayList<Course>();
+
+    public Professor(Department department, String name) {
+        this.name = name;
+        dpart = department;
+    }
+
+    public Department getDepartment() {
+        return dpart;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public Course[] getCourses() {
+        return null;
+    }
+}

src/com/university/Student.java

+package com.university;
+
+import java.util.ArrayList;
+
+public class Student {
+    private String name;
+    private String ID;
+    private String major;
+    private Department dpart;
+    private ArrayList<Course> crss = new ArrayList<Course>();
+
+
+    public Student(String name, String ID, String major, Department department) {
+
+        this.name = name;
+        this.ID = ID;
+        this.major = major;
+        dpart = department;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public String getID() {
+        return ID;
+    }
+
+    public String getMajor() {
+        return major;
+    }
+
+    public Department getDepartment() {
+        return dpart;
+    }
+
+    public Course[] getCourses() {
+        Course[] courses = crss.toArray(new Course[crss.size()]);
+        return courses;
+    }
+
+    public void addCourse(Course course){
+        if(course != null) {
+            crss.add(course);
+        }
+    }
+}

src/com/university/StudnetTest.java

+package com.university;
+
+import org.junit.Test;
+import org.junit.jupiter.api.BeforeAll;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotNull;
+
+
+public class StudnetTest {
+    static Student student;
+    static Department department;
+
+    @BeforeAll
+    public static void createStudent(){
+        department = new Department("Computer and IT Eng");
+        student = new Student("Alireza", "1234", "Software Eng", department);
+    }
+
+    @Test
+    public void testStudentGetName(){
+
+        assertEquals("Alireza", student.getName());
+    }
+
+    @Test
+    public void testStudenGetCourses(){
+        assertNotNull(student.getCourses());
+        assertEquals(0, student.getCourses().length);
+    }
+
+}

src/com/university/University.java

+package com.university;
+
+public class University {
+    public Department[] getDepartments(){
+        return null;
+    }
+
+    public void addDepartment(Department department){ }
+
+    public void removeDepartment(Department department){ }
+}

src/com/university/test.java

+package com.university;
+
+public class test {
+    public static void main(String[] args){
+        Department dp = new Department("amirkabir");
+        Student st = new Student("Mohammad" , "1234" , "Mechanic" , dp);
+        System.out.println(st.getName());
+    }
+
+}

src/test/StudnetTest.java

+package test;
+
+
+import com.university.Course;
+import com.university.Department;
+import com.university.Professor;
+import com.university.Student;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+
+import static junit.framework.TestCase.assertEquals;
+import static junit.framework.TestCase.assertNotNull;
+
+public class StudnetTest {
+    static Student student , student1;
+    static Department department;
+    static Professor prf;
+
+    @BeforeAll
+    public static void createStudent(){
+        department = new Department("Computer and IT Eng");
+        student = new Student("Alireza", "1234", "Software Eng", department);
+        prf = new Professor(department , "Ohadi");
+        Course c1 = new Course("12" , "mathematic" , department , prf , 1);
+        Course c2 = new Course("14" , "Physic" , department , prf , 2);
+        student1 = new Student("Mohammad" , "4321" , "Mechanic" , department);
+        student1.addCourse(null);
+
+    }
+
+    @Test
+    public void testStudentGetName(){
+
+        assertEquals("Alireza", student.getName());
+    }
+
+    @Test
+    public void testStudenGetCourses(){
+        assertNotNull(student.getCourses());
+        assertEquals(0, student.getCourses().length);
+    }
+    @Test
+    public void testStudentID(){
+        assertNotNull(student.getID());
+    }
+    @Test
+    public void testStudentDepartment(){
+        assertNotNull(student.getDepartment());
+    }
+    @Test
+    public void testStudentMajor(){
+        assertNotNull(student.getMajor());
+    }
+    @Test
+    public void testStudentNullCourse(){
+        assertEquals(0 , student1.getCourses().length);
+    }
+
+}