public async Task DeleteCategoryAsyncTest()
        {
            var options = new DbContextOptionsBuilder <ApplicationDbContext>()
                          .UseInMemoryDatabase(databaseName: Guid.NewGuid().ToString()).Options;
            var dbContext = new ApplicationDbContext(options);

            dbContext.Categories.Add(
                new Category
            {
                Id   = 1,
                Name = "Test1",
            });
            dbContext.Categories.Add(
                new Category
            {
                Id   = 2,
                Name = "Test2",
            });
            await dbContext.SaveChangesAsync();

            var repository = new EfDeletableEntityRepository <Category>(dbContext);
            var service    = new CategoriesService(repository);
            await service.DeleteCategoryAsync(1);

            Assert.Single(service.AllCategoryNames());
        }