NimbleMock

Zero-allocation, source-generated C# mocking library for exceptional developer experience.

Why NimbleMock?

34x faster than Moq, 7x faster than NSubstitute in mock creation. 67% less memory allocation.

// Before (Moq) - 48,812ns, 10.37 KB
var mock = new Mock<IUserRepository>();
mock.Setup(x => x.GetById(1)).Returns(user);
mock.Setup(x => x.SaveAsync(It.IsAny<User>())).ReturnsAsync(true);
var repo = mock.Object;

// After (NimbleMock) - 1,415ns, 3.45 KB
var mock = Mock.Of<IUserRepository>()
    .Setup(x => x.GetById(1), user)
    .SetupAsync(x => x.SaveAsync(default!), true)
    .Build();

Key Features

• ✅ Stack-allocated builders with arrays - zero GC pressure
• ✅ Source generators create compile-time proxies (no Castle.DynamicProxy)
• ✅ Fluent API with intelligent type inference
• ✅ First-class async support (Task<T>, ValueTask<T>)
• ✅ Partial mocks for large interfaces
• ✅ Roslyn analyzers detect unverified calls at compile-time
• ✅ No telemetry (looking at you, Moq)

Installation

dotnet add package NimbleMock

Quick Start

using NimbleMock;
using Xunit;

public interface IUserRepository
{
    User GetById(int id);
    Task<bool> SaveAsync(User user);
}

public class UserServiceTests
{
    [Fact]
    public void GetUser_ReturnsFromRepository()
    {
        // Arrange
        var expectedUser = new User { Id = 1, Name = "Alice" };
        var mock = Mock.Of<IUserRepository>()
            .Setup(x => x.GetById(1), expectedUser)
            .Build();

        var service = new UserService(mock.Object);

        // Act
        var result = service.GetUser(1);

        // Assert
        Assert.Equal(expectedUser, result);
        mock.Verify(x => x.GetById(1)).Once();
    }
}