new_contents: from datetime import datetime
  
  from django.test import TestCase
  
  from students.models import Student, Group, Exam, MonthJournal
  
  
  class TestStudentModel(TestCase):
      """Test for Student model"""
  
      def test_str(self):
          student = Student(first_name='Test', last_name='Student')
          self.assertEqual(str(student), 'Test Student')
  
  
  class TestGroupModel(TestCase):
      """Test for Group model"""
  
      def test_str(self):
          group = Group(title='Some Title')
          self.assertEqual(str(group), 'Some Title')
  
          student = Student(id=1, first_name='Test', last_name='Student')
          group2 = Group(title='Another Title', leader=student)
          self.assertEqual(str(group2), 'Another Title (Test Student)')
  
  
  class TestExamModel(TestCase):
      """Test for Exam model"""
  
      def test_str(self):
          exam = Exam(subject='Test', date='2017-11-11')
          self.assertEqual(str(exam), 'Test (2017-11-11)')
  
          group = Group(title='Some Title')
          exam2 = Exam(subject='Test2', group=group, date='2017-10-10')
          self.assertEqual(str(exam2), 'Some Title, Test2 (2017-10-10)')
  
  
  class TestJournalModel(TestCase):
      """Test for MonthJournal model"""
  
      def test_str(self):
          student = Student(first_name='Test', last_name='Student')
          journal = MonthJournal(student=student, date=datetime(2017, 10, 10))
          self.assertEqual(str(journal), 'Student: 10, 2017')
  
subject: create tests for models