public void ExistsInvoice_Exists()
        {
            var options = new DbContextOptionsBuilder <InvoiceContext>()
                          .UseInMemoryDatabase(databaseName: "ExistsInvoice_Exists")
                          .Options;

            using (var context = new InvoiceContext(options))
            {
                context.Invoices.AddRange(
                    new Invoice {
                    InvoiceId = new Guid("050b2d01-67a4-417c-9ef2-625aaa4d81b9"), Amount = 1.1m
                },
                    new Invoice {
                    InvoiceId = new Guid("777a1a81-3115-474d-9c43-ed103a091eba"), Amount = 2.2m
                },
                    new Invoice {
                    InvoiceId = new Guid("872db39e-19f5-4be9-8870-29c80c93eb4d"), Amount = 3.3m
                }
                    );
                context.SaveChanges();
            }

            using (var context = new InvoiceContext(options))
            {
                var repository = new EntityFrameworkInvoiceRepository(context);
                var exists     = repository.ExistsInvoice(new Guid("777a1a81-3115-474d-9c43-ed103a091eba"));
                Assert.IsTrue(exists);
            }
        }
        public void ExistsInvoice_NotExists()
        {
            var options = new DbContextOptionsBuilder <InvoiceContext>()
                          .UseInMemoryDatabase(databaseName: "ExistsInvoice_NotExists")
                          .Options;

            using (var context = new InvoiceContext(options))
            {
                var repository = new EntityFrameworkInvoiceRepository(context);
                var exists     = repository.ExistsInvoice(new Guid("050b2d01-67a4-417c-9ef2-625aaa4d81b9"));
                Assert.IsFalse(exists);
            }
        }