public void TeacherControllerAssignExamToGroupTest()
        {
            //Arrange
            bool isExamAssigned = false;

            var group = new Mock <Group>("Test");

            group.Setup(t => t.AssignExam(It.IsAny <Exam>())).Callback(() => isExamAssigned = true);

            Teacher           teacher           = new Teacher("Petro", "Petrov", "ID", "petrov");
            TeacherController teacherController = new TeacherController(teacher);
            Exam exam = new Exam("SomeExam", 1, 3, 1);

            //Act
            teacherController.AssignExamToGroup(exam, group.Object);

            //Assert
            Assert.IsTrue(isExamAssigned);
        }