Fast and Memory-Efficient Mocking Library

Imposter is a mocking library that's using roslyn source generators to achieve high performance and low memory footprint.

Visit the Docs for more information

🚀 Quick Start

Add nuget package reference:

dotnet add package Imposter

Pick an interface or non-sealed class that you would like to generate an imposter for.

Say we have a below interface

namespace Application.Domain;

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

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

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

Then use can use the generated imposter in your tests

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

Learn more: https://themidnightgospel.github.io/Imposter/

✨ Feature-Rich

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

⏱️ Benchmark

We benchmarked the simple method-impersonation scenario: we set up a Square method to return input * input and ran it for 1, 10, 100, and 1000 iterations.

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

Mean execution time

Method	Iteration	Mean
Moq	1	69,346.1 ns
NSubstitute	1	1,976.2 ns
FakItEasy	1	2,006.7 ns
Imposter	1	194.3 ns
Moq	10	686,282.9 ns
NSubstitute	10	11,201.6 ns
FakItEasy	10	12,399.0 ns
Imposter	10	1,896.7 ns
Moq	100	6,804,897.3 ns
NSubstitute	100	335,390.6 ns
FakItEasy	100	258,220.2 ns
Imposter	100	34,011.7 ns
Moq	1000	99,710,929.5 ns
NSubstitute	1000	26,986,939.0 ns
FakItEasy	1000	18,997,374.5 ns
Imposter	1000	2,452,970.7 ns

Allocated Memory

Method	Iteration	Allocated
Moq	1	13.05 KB
NSubstitute	1	7.84 KB
FakeItEasy	1	5.84 KB
Imposter	1	2.4 KB
Moq	10	115.73 KB
NSubstitute	10	29.29 KB
FakeItEasy	10	38.81 KB
Imposter	10	22.37 KB
Moq	100	1416.91 KB
NSubstitute	100	247.26 KB
FakeItEasy	100	1033.38 KB
Imposter	100	222.05 KB
Moq	1000	42275.19 KB
NSubstitute	1000	2420.82 KB
FakeItEasy	1000	77101.74 KB
Imposter	1000	2218.93 KB

Benchmark Environment

BenchmarkDotNet v0.15.6, Windows 11 (10.0.26200.6899)
13th Gen Intel Core i9-13900HX 2.20GHz, 1 CPU, 32 logical and 24 physical cores
.NET SDK 10.0.100
[Host]     : .NET 8.0.21 (8.0.21, 8.0.2125.47513), X64 RyuJIT x86-64-v3
DefaultJob : .NET 8.0.21 (8.0.21, 8.0.2125.47513), X64 RyuJIT x86-64-v3

See other benchmarks benchmark

Docs

Docs: https://themidnightgospel.github.io/Imposter/

License

Licensed under the MIT License. See LICENSE.txt for details.