public async Task OnPageAsync_MentorIsNull() { #region Arrange var optionsBuilder = new DbContextOptionsBuilder <ApplicationDbContext>() .UseInMemoryDatabase("InMemoryDb"); var mockDb = new Mock <ApplicationDbContext>(optionsBuilder.Options); var expectedUsers = ApplicationDbContext.GetSeedMentor(); var expectedUser = expectedUsers.FirstOrDefault(); expectedUser.Mentor = null; var username = expectedUser.UserName; mockDb.Setup(db => db.GetMentorAsync(username)) .Returns(Task.FromResult(expectedUser)); var pageModel = new AddressModel(mockDb.Object); pageModel.Username = username; pageModel.AddressMentor = ApplicationDbContext.GetSeedAddresses() .FirstOrDefault(); #endregion #region Act var result = await pageModel.OnPostAsync(); #endregion #region Assert Assert.IsType <NotFoundObjectResult>(result); #endregion }