public async Task TestAddTeacher() { DbContextOptions <ApplicationDbContext> options = new DbContextOptionsBuilder <ApplicationDbContext>() .UseInMemoryDatabase(databaseName: "TestAddTeachersDb").Options; using var dbContext = new ApplicationDbContext(options); dbContext.Database.EnsureDeleted(); using var repository = new EfDeletableEntityRepository <Teacher>(dbContext); var service = new UsersService(repository, null, null); dbContext.Teachers.Add(new Teacher() { Id = 1, ApplicationUserId = "one" }); dbContext.Teachers.Add(new Teacher() { Id = 2, ApplicationUserId = "two" }); dbContext.Teachers.Add(new Teacher() { Id = 3, ApplicationUserId = "three" }); await dbContext.SaveChangesAsync(); await service.AddTeacher(new ApplicationUser() { Id = "newUser" }); Assert.Equal(4, dbContext.Teachers.Count()); }