We’ve all worked on projects where the intended architecture slowly erodes over time. Layer boundaries blur, dependencies creep in where they shouldn’t, and before long, the clean structure you started with is hard to recognize. This architectural drift is subtle, but it can lead to tangled code, harder maintenance, and costly bugs.

This post will show you how to enforce your intended architecture using architecture tests. By writing automated tests that validate your architectural rules, you can catch violations early, keep your codebase healthy, and make your intentions clear to everyone on the team.

A Hidden Problem: Architecture Erosion

Imagine a typical layered application with Domain, Application, and Infrastructure projects. The intended rule is simple: Domain should not depend on Application or Infrastructure, and Application should not depend on Infrastructure.

But as the codebase grows, it’s easy for someone to accidentally introduce a dependency in the wrong direction. For example:

// In Domain project
using Infrastructure.SomeService; // Oops! Domain should not reference Infrastructure

public class OrderService
{
    // ...existing code...
}

This kind of mistake is easy to make and hard to spot in code reviews—especially in large teams or over time.

A Safer Approach: Architecture Tests

Instead of relying on documentation or tribal knowledge, you can write architecture tests that automatically check your dependency rules. In .NET, libraries like NetArchTest make this straightforward.

For example, you can write a test to ensure that the Domain project does not reference Infrastructure:

using NetArchTest.Rules;
using Xunit;

public class ArchitectureTests
{
    [Fact]
    public void Domain_Should_Not_Have_Dependencies_On_Infrastructure()
    {
        var result = Types
            .InAssembly(typeof(Domain.SomeType).Assembly)
            .ShouldNot()
            .HaveDependencyOn("Infrastructure")
            .GetResult();

        Assert.True(result.IsSuccessful, "Domain should not depend on Infrastructure");
    }
}

Now, if someone accidentally introduces a forbidden dependency, the test will fail—alerting you before the problem spreads.

Why Architecture Tests Matter

Architecture tests offer several key benefits:

• Automated Enforcement: Rules are checked on every build or CI run, not just in code reviews.
• Clarity: Architectural intent is codified and visible to everyone.
• Confidence: Refactoring is safer when you know tests will catch accidental violations.
• Maintainability: Prevents architectural drift and keeps your codebase healthy over time.

Final Thoughts

Architecture tests are a lightweight but powerful tool for keeping your codebase aligned with your intended design. By making architectural rules explicit and enforceable, you reduce the risk of accidental erosion and make your system easier to maintain. If you care about long-term code quality, architecture tests are well worth the small investment.