public async Task DeleteAllAsync_Success()
        {
            // Arrange
            var items = new List <Author>()
            {
                new Author()
                {
                    Name = "name", Surname = "surname", BornDate = "01-01-1970", Country = "TEST"
                },
                new Author()
                {
                    Name = "name1", Surname = "surname1", BornDate = "01-01-1970", Country = "TEST"
                },
                new Author()
                {
                    Name = "name2", Surname = "surname2", BornDate = "01-01-1970", Country = "TEST"
                }
            };

            items.ForEach(x => db.AddItemAsync(x).ConfigureAwait(true));
            Assert.AreEqual(items.Count, db.GetItemsAsync().Result.Count);


            // Act
            await db.DeleteAllAsync();

            // Assert
            Assert.AreEqual(0, db.GetItemsAsync().Result.Count);
        }