Clean Architecture and MediatR

What they ask

The on-site technical round is long, one to two hours, and most of it is a design conversation rather than live coding. The backend is .NET, and the recurring theme is Clean Architecture and the Mediator pattern: how you have used them, where they helped, and where they got in the way.

Expect a prompt along these lines:

Design the backend module for a savings circle (gam3eya): members join a circle, pay monthly, and one member receives the payout each cycle. Show me the layers, the use cases, and how a PayInstallment request flows through the system.

They then go deep on specifics:

• Which layer owns the rule "a member cannot receive the payout before completing their payments", and why.
• How a MediatR request handler, a pipeline behavior for validation, and the domain entities relate.
• What happens when two handlers must touch the same aggregate in one transaction.
• What you would not put behind the mediator.

They also ask about the technical work at your current company in real detail: what you built, what you would change, and how you made architectural decisions.

What they look for

• The dependency rule stated correctly: domain at the centre, application use cases around it, infrastructure and web on the outside.
• Pragmatism. Saying "for a small CRUD module this is overkill" is a good sign, not a bad one.
• Concrete experience with CQRS-style handlers, validation behaviors, and unit-testing a handler in isolation.
• Money handling instincts: idempotent payment commands, decimal types, an audit trail.

The interviewers are described as friendly and the round conversational, so ask questions back.