Getting Started

What is Skugga?

Skugga (Swedish for Shadow) is a mocking library engineered specifically for Native AOT and Cloud-Native .NET. It moves mocking logic from runtime reflection to compile-time code generation, making it 100% AOT-compatible with zero overhead.

Legacy tools like Moq rely on System.Reflection.Emit to generate proxy objects at runtime. Since Native AOT strips away the JIT compiler, these tools crash instantly. Skugga eliminates this trade-off by generating mock implementations during the build process.

Installation

1. Install Skugga

dotnet add package Skugga

Requirements

• .NET 8.0 or later
• C# 12 enabled (LangVersion 12 or latest)

2. Enable Interceptors

Add the following to your test project's .csproj:

<PropertyGroup>
   <InterceptorsPreviewNamespaces>$(InterceptorsPreviewNamespaces);Skugga</InterceptorsPreviewNamespaces>
</PropertyGroup>

Writing Your First Test

using Skugga.Core;

public interface IEmailService
{
   string GetEmailAddress(int userId);
   string TenantName { get; }
}

public class MyFirstTest
{
   public void Run()
   {
       // 1. Create the mock (intercepted at compile time)
       var mock = Mock.Create<IEmailService>();

       // 2. Configure behavior
       mock.Setup(x => x.GetEmailAddress(1)).Returns("digvijay@digvijay.dev");
       mock.Setup(x => x.TenantName).Returns("Contoso");

       // 3. Execute
       var email = mock.GetEmailAddress(1); // Returns "digvijay@digvijay.dev"
       var tenant = mock.TenantName;        // Returns "Contoso"
   }
}

How It Works

Skugga leverages C# 12 Interceptors to seamlessly rewire your code during compilation:

1. Scan -- The Source Generator detects calls to Mock.Create<T>().
2. Generate -- It writes a concrete, optimized C# class (Skugga_T) that implements T.
3. Intercept -- The compiler replaces your Mock.Create call with new Skugga_T().

Zero Friction: To the developer, it looks like a normal method call. To the runtime, it looks like hand-written, optimized code.

Next Steps

• Mock Creation -- Explore all ways to create mocks
• Setup & Returns -- Configure mock behavior
• Verification -- Assert method calls happened
• Migrating from Moq -- Seamless migration guide
• Architecture -- Deep dive into how Skugga works