Imposter 1.0.3

<p align="center"> <img src="docs/imposter_logo.png" alt="Imposter logo" width="140" /> </p>

<p align="center"> Mocking library with the perfect balance of Performance and Intuitive API </p>

🧘Balanced Performance and Developer Experience

Imposter delivers top-tier performance without sacrificing a natural, intuitive API. While being ~10× faster than NSubstitute and up to ~50× faster than Moq in common mocking scenarios, Imposter is not the fastest mocking library available. Instead, it focuses on achieving a balance between performance and API ease of use.

🚀 Quick Start

Add nuget package reference:

dotnet add package Imposter

Pick a target

namespace Application.Domain;

public interface ICalculator
{
    int Add(int a, int b);
}

Use [GenerateImposter] attribute in your tests project, this will generate an imposter

[assembly: GenerateImposter(typeof(Application.Domain.ICalculator))]

Use the generated imposter

using System.Threading.Tasks;
using Imposter.Abstractions;

// c# 14
var imposter = ICalculator.Imposter();

// c# 9 - 13
// var imposter = new ICalculatorImposter();

imposter.Add(Arg<int>.Any(), Arg<int>.Any())
    .Returns(1)
    .Then()
    .Returns(2);

var calculator = imposter.Instance();

calculator.Add(1, 2); // 1
calculator.Add(1, 2); // 2

🛡️ Strongly typed all the way

Loosely typed callbacks can easily cause runtime exceptions. Imposter enforces strong typing across the entire mocking pipeline, eliminating type mismatch errors for good. See more here

🎭 Interfaces and classes

Not limited to interfaces — Imposter can impersonate non-sealed classes and their protected members. See more here

🧬 Full generic support

Generics are fully supported. see more here

🧩 Mock any member

Imposter supports not only methods, but also properties, events and indexers.

🔀 Implicit and Explicit Modes

Choose how unmocked members behave. Implicit mode returns defaults silently — great for prototyping. Explicit mode throws on any call without a setup — ideal for unit tests that must be precise. See more here

🧵 Thread-safe by design

Imposter is built to work reliably in multi-threaded and parallel test environments.

⏱️ Benchmark

Each library sets up Square to return input * input and calls it, for 1, 10, 100 and 1,000 iterations. See benchmarks for the code.

public interface ICalculator
{
    int Square(int input);
}

The Benchmarks workflow reruns this comparison on a GitHub-hosted runner after every change to the code on master, so the table always shows the latest build. Shared runners are slower and noisier than a desktop machine: compare the libraries within the table rather than the absolute timings. The same results are available as Markdown.

✨ Feature-Rich

• Method Impersonation
• Property Impersonation
• Indexer Impersonation
• Event Impersonation
• Class Impersonation
• Generics
• Implicit & Explicit Modes
• Use Base implementation
• Async Support
• Protected members Impersonation

Docs

• See Docs

📜 MIT License

Free to use, modify, and distribute under the MIT License.