Testing a MVC Controller fails with NULL reference exception

Question

Below is the setup that I am trying to test.

The controller:

public ActionResult UpsertStudent(StudentModel studentModel)
{
    try
         


        

Answer 1

I am not sure if I have understood you problem correctly, but looking at the code snippets provided, the test will go and hit the database, because the mock object and its expectation is not defined.

I would have implemented the solution like this -

I am making some assumptions that your _updateStudentManager object is for the class that is doing the DB interaction for Student. I'll call it say StudentRepository. And to allow you to mock the behavior I would make it Interface driven. So typically my setup would look like this -

//Interface
public interface IStudentrepository
{
    StudentModel GetStudentInfo(int studentId);
}

//Class implementing IStudentrepository
public class StudentRepository : IStudentrepository
{
    public StudentModel GetStudentInfo(int studentId)
    {
        //Implementation goes here
    }
}

Now in my controller, I would have an instance of IStudentrepository, which can be injected via constructor.

public class StudentController
{
    private readonly IStudentrepository updateStudentManager;
    public StudentController(IStudentrepository updateStudentManager)
    {
        this.updateStudentManager = updateStudentManager;
    }
}
//Rest of the code for controller....

Now while writing my Test, I will create a mock object of IStudentrepository, define the expectation for the mock object, and inject it when creating the controller object. Something like this.

    [TestMethod]
    public void TestMethod1()
    {
        //--Arrange--
        //Define a mock object for student repository
        var mock = new Mock<IStudentrepository>();

        //Define the expectations of the mock object
        mock.Setup(s => s.GetStudentInfo(It.IsAny<int>()))
            .Returns(new StudentModel {/*return the required object */ });

        //Instantiate controller and inject the mock object
        StudentController _controller = new StudentController(mock.Object);

        //--Act--
        var res = _controller.UpsertStudent(studentModel) as JsonResult;


        //--Assert--
        if (res != null) Assert.AreEqual("{ result = True }", res.Data.ToString());

    }

Now when your test method calls the GetStudentInfo method, instead of hitting the db, it will return the value as set in mock object.

This is just a high level implementation, and of course you can modify it as per your design. Hope it helps