public void AddPhoneToUserShouldChangeOrAddPhoneToUser() { DbContextOptions <UltimateMoviesDbContext> options = new DbContextOptionsBuilder <UltimateMoviesDbContext>() .UseInMemoryDatabase(databaseName: "Users_AddPhoneToUser_Database") .Options; UltimateMoviesDbContext db = new UltimateMoviesDbContext(options); IUsersService usersService = new UsersService(db); db.Users.Add(new UMUser { UserName = "******" }); db.SaveChanges(); usersService.AddPhoneToUser("Tester", "080011100"); Assert.Equal("080011100", db.Users.Last().PhoneNumber); }