public async Task AllConfirmedAsync_ShouldReturnsCorrectCountOfConfirmedSubscribers()
        {
            await this.dbContext.Subscribers.AddRangeAsync(new List <Subscriber>
            {
                new Subscriber {
                    IsConfirmed = true
                },
                new Subscriber {
                    IsConfirmed = false
                },
                new Subscriber {
                    IsConfirmed = true
                },
                new Subscriber {
                    IsConfirmed = true
                },
                new Subscriber {
                    IsConfirmed = false
                },
            });

            await this.dbContext.SaveChangesAsync();

            var subscriberService = new SubscriberService(this.dbContext);

            var result = await subscriberService.AllConfirmedAsync <FakeSubscriber>();

            var expectedCount = 3;
            var actualCount   = result.Count();

            Assert.Equal(expectedCount, actualCount);
        }