Why should you care?

ShopNest NotificationService tests verify email sent after order — mock IOrderRepository to return order without EF.

See it live — copy this example

Paste into a .NET project with EF Core packages, then run with LocalDB/SQL Server (dotnet ef / dotnet run).

var orderRepo = new Mock<IOrderRepository>();
orderRepo.Setup(r => r.GetByIdAsync(42, It.IsAny<CancellationToken>()))
    .ReturnsAsync(new Order { Id = 42, CustomerId = 7 });

var uow = new Mock<IUnitOfWork>();
uow.Setup(u => u.Orders).Returns(orderRepo.Object);

var svc = new OrderNotificationService(uow.Object, emailSender);
await svc.SendConfirmationAsync(42, CancellationToken.None);

emailSender.Verify(e => e.SendAsync(It.IsAny<string>(), It.IsAny<string>()), Times.Once);

What happened?

• Moq configures GetByIdAsync return.
• Service under test never touches EF.
• Verify email sender called once — behavior assertion.

Practice next

1. Mock interfaces Application already uses — not DbSet directly.
2. Setup ReturnsAsync with realistic domain objects.
3. Verify interactions when testing side effects.
4. Use NSubstitute Returns syntax for same test.
5. Mock IUnitOfWork.SaveChangesAsync to verify commit called.

Remember

Mock repository interfaces not DbContext. Moq/NSubstitute configure async returns. Pair with few integration tests for EF paths.

ShopNest email unit test

OrderNotificationService tested with mocked IOrderRepository and IEmailSender.

Outcome: Email template logic covered without SMTP or SQL in unit test job.