Building Testable and Modular Applications with .NET Clean Architecture

One of the primary goals of Clean Architecture is to make your application testable and modular. This article will discuss how to structure .NET projects for testability, implement dependency inversion, and use mocking for unit tests effectively.

Structuring Projects for Testability

A well-organized project structure is the foundation of a testable application. In Clean Architecture, the structure typically includes these layers:

1. Core Layer: Contains business logic (Entities and Use Cases).
2. Application Layer: Contains interfaces and service abstractions.
3. Infrastructure Layer: Contains implementations for database and external services.
4. Presentation Layer: Contains APIs, UI, or other front-facing code.

Implementing Dependency Inversion

Dependency inversion ensures that high-level modules are not dependent on low-level modules but on abstractions.

Example: Using Interfaces for Repositories

public interface ICustomerRepository
{
    Task<Customer> GetByIdAsync(int id);
    Task AddAsync(Customer customer);
}

Implementation

public class CustomerRepository : ICustomerRepository
{
    private readonly AppDbContext _context;

    public CustomerRepository(AppDbContext context)
    {
        _context = context;
    }

    public async Task<Customer> GetByIdAsync(int id)
    {
        return await _context.Customers.FindAsync(id);
    }

    public async Task AddAsync(Customer customer)
    {
        await _context.Customers.AddAsync(customer);
        await _context.SaveChangesAsync();
    }
}

Injecting Dependencies

services.AddScoped<ICustomerRepository, CustomerRepository>();

Unit Testing with Mocking

Mocking external dependencies is critical for isolating units of work in tests.

1. Setting Up Unit Tests Use frameworks like Moq for mocking dependencies.

Test Case: Validating Customer Service

[Fact]
public async Task GetCustomerById_ShouldReturnCustomer()
{
    // Arrange
    var mockRepo = new Mock<ICustomerRepository>();
    mockRepo.Setup(repo =>…