public async Task DeleteByIdAsync_Deletes_ContactAsync()
        {
            using (var dbContext = ContactDbContextInMemory.CreateInMemoryDbContext())
            {
                //Arrange
                var contact1 = new Contact {
                    Id = 9, FirstName = "test1"
                };
                var contact2 = new Contact {
                    Id = 10, FirstName = "test2"
                };
                var contact3 = new Contact {
                    Id = 11, FirstName = "test3"
                };

                dbContext.Contacts.Add(contact1);
                dbContext.Contacts.Add(contact2);
                dbContext.Contacts.Add(contact3);
                dbContext.SaveChanges();

                //Act
                var sut = new ContactRepository(dbContext);
                await sut.DeleteByIdAsync(9, It.IsAny <CancellationToken>());

                var result = sut.GetByIdAsync(9, It.IsAny <CancellationToken>());

                //Assert
                Assert.Null(result.Result);
            }
        }