public void Add_InvalidObjectPassed_ReturnsBadRequest()
        {
            // Arrange
            var nameMissingItem = new SubjectModel()
            {
                Credits   = 3,
                TeacherId = 1
            };

            studentsController.ModelState.AddModelError(nameof(nameMissingItem.Name), "Required");
            // Act
            var badResponse = studentsController.PostSubject(nameMissingItem).Result;

            // Assert
            Assert.IsType <BadRequestObjectResult>(badResponse.Result);
        }