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
}