How to Insert Dependency Injection in mvc project - asp.net-mvc

Question

I have Added Unit Testing in Existing MVC project and also added references
when i create object of controller
it throws an Exception due to DBContext context object i created in MVC but I need to do Dependency Injection and mocking so that it will not check for it.
please how can i make interface of db to do dependency injection.
code in mvc
public class TestingController : Controller
{
//
// GET: /Testing/
ApplicationDbContext db = new ApplicationDbContext();
Random rnd = new Random();
[Authorize]
public ActionResult Index()
{
string uName = User.Identity.GetUserName();
QuestionsViewModel vm = new QuestionsViewModel();
List<AddQuestion> adlist = new List<AddQuestion>();
List<QuestionsViewModel> qlist = new List<QuestionsViewModel>();
List<int> rn = new List<int>();
List<int> rn2 = new List<int>();
List<int> rn3 = new List<int>();
AddQuestion adq = new AddQuestion();
var Sessionid = System.Guid.NewGuid();
vm.sessionid = Sessionid.ToString();
Session["ApplicantSession"] = Sessionid.ToString();
ViewBag.StartTime = Session.Timeout;
List<List<int>> threecompQids = new List<List<int>>();
List<int> c1question = db.AddQuestions.Where(x => x.ComplexityLevel == 1)
.Select(y => y.AddQuestionID).ToList();
List<int> c2question = db.AddQuestions.Where(x => x.ComplexityLevel == 2)
.Select(y => y.AddQuestionID).ToList();
List<int> c3question = db.AddQuestions.Where(x => x.ComplexityLevel == 3)
.Select(y => y.AddQuestionID).ToList();
for (int i = 0; i < 5; i++)
{
int r = rnd.Next(c1question.Min(), c1question.Max() + 1);
while (!(c1question.Any(w => w.Equals(r)) && !rn.Any(w => w == r)))
{
r = rnd.Next(c1question.Min(), c1question.Max() + 1);
}
rn.Add(r);
r = rnd.Next(c2question.Min(), c2question.Max() + 1);
while (!(c2question.Any(w => w.Equals(r)) && !rn2.Any(w => w == r)))
{
r = rnd.Next(c2question.Min(), c2question.Max() + 1);
}
rn2.Add(r);
r = rnd.Next(c3question.Min(), c3question.Max() + 1);
while (!(c3question.Any(w => w.Equals(r)) && !rn3.Any(w => w == r)))
{
r = rnd.Next(c3question.Min(), c3question.Max() + 1);
}
rn3.Add(r);
}
var fstquestion = rn[0];
threecompQids.Add(rn);
threecompQids.Add(rn2);
threecompQids.Add(rn3);
vm.ComplexLevQidsLists = threecompQids;
adq = db.AddQuestions.Find(fstquestion);
List<Option> opt = db.Options.Where(op => op.AddQuestionID == adq.AddQuestionID).ToList();
vm.Questions = adq;
vm.Options = opt;
vm.UserName = uName;
return View(vm);
}
}
where as in test project i only created object of testcontroller

Answer 1

It seems like you didn't mock data access component your controller depends on, right? If this is the case and you are using actual implementation in your unit test, most likely your connection string defined in Test project is missing or differs from the connection string defined in MVC project.
Also keep in mind that if you do not mock your controller's dependencies, your unit test is technically cannot be considered as "unit" — it's more like an integration or scenario test.

Answer 2

You should either abstract the ApplicationDbContext using an interface like IAppDbContext or provide the connection string to the testing project too. In the latter case your test will stop being unit test though.
public class MyController: Controller
{
IAppDbContext _context;
pulbic MyController(IAppDbContext context)
{
_context = context; // Now you can use the interface to perform your data access operations
}
....
}
And now you will be able to inject mock implementations of IAppDbContext in your unit tests.
You should do some research on Dependency Inversion and Mocking.