Decoupling Logic for Verifiable Unit Tests

Snippet

Decoupling Logic for Verifiable Unit Tests

To make code testable, dependencies (like a message service) should be passed via interfaces rather than instantiated directly. This pattern, combined with C# 12 primary constructors, allows you to easily inject 'mock' objects during testing to verify logic in isolation.

snippet.cs

csharp

public interface IMessageService { void Send(string msg); }
 
public class OrderProcessor(IMessageService service)
{
    public void CompleteOrder(int id)
    {
        // Business logic here...
        service.Send($"Order {id} completed.");
    }
}
 
// In test: Create a mock implementation of IMessageService
// to verify Send was called without sending real emails.

Breakdown

public class OrderProcessor(IMessageService service)

Uses a primary constructor to declare and receive the dependency.

service.Send($"Order {id} completed.");

The logic depends on the abstraction (interface), making it easy to swap for a test double.

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Decoupling Logic for Verifiable Unit Tests

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