Conjecture.Mcp

What is it?

Hypothesis's engine, reimagined for idiomatic C#. Write tests that describe what your code should do, and let Conjecture generate hundreds of random inputs to find the edge cases you'd never think of. When it finds a failure, it automatically shrinks the input to the smallest possible counterexample — no hand-written cases required.

Install

Pick the adapter for your test framework:

dotnet add package Conjecture.Xunit      # xUnit v2
dotnet add package Conjecture.Xunit.V3   # xUnit v3
dotnet add package Conjecture.NUnit      # NUnit
dotnet add package Conjecture.MSTest     # MSTest

Quick Example

using Conjecture.Xunit;

public class SortTests
{
    [Property]
    public bool Sorting_is_idempotent(List<int> items)
    {
        List<int> sorted = items.OrderBy(x => x).ToList();
        List<int> sortedTwice = sorted.OrderBy(x => x).ToList();
        return sorted.SequenceEqual(sortedTwice);
    }
}

Run with dotnet test. Conjecture generates random lists, runs the property 100 times, and if it fails, shrinks the input to the minimal failing case.

Features

• Automatic test generation — generates random inputs from type-aware strategies
• Intelligent shrinking — finds the smallest failing input via byte-stream minimization
• LINQ composition — build complex strategies with Select, Where, SelectMany
• All major test frameworks — xUnit v2, xUnit v3, NUnit, MSTest, Microsoft Testing Platform
• F# support — idiomatic Gen<'a> wrapper plus an Expecto integration
• Source generators — derive strategies for your types with [Arbitrary]
• Roslyn analyzers — catch common mistakes at compile time
• Stateful testing — model systems as state machines and explore command sequences
• Targeted testing — steer generation toward extremes with Target.Maximize / Target.Minimize
• Recursive strategies — generate bounded-depth trees and self-referential types
• Example database — persist failing inputs for automatic regression prevention
• Reproduction export — write a runnable .cs repro of any failing input via ExportReproductionOnFailure
• Structured logging — structured events for generation, shrinking, and targeting phases
• HTTP / gRPC / messaging / EF Core / ASP.NET Core / Aspire integrations — model real distributed systems as IInteractionTargets and dispatch composed interactions through one state machine
• MCP server + dotnet tool — generate strategies and standalone test data from the CLI or AI assistants

Packages

Package	Purpose
Test adapters
Conjecture.Core	Core engine, analyzers, source generator. Required by every adapter.
Conjecture.Xunit	xUnit v2 adapter.
Conjecture.Xunit.V3	xUnit v3 adapter.
Conjecture.NUnit	NUnit adapter.
Conjecture.MSTest	MSTest adapter.
Conjecture.TestingPlatform	Microsoft Testing Platform adapter.
Domain strategies
Conjecture.Time	Boundary-aware DateTimeOffset, DST/leap edges, FakeTimeProvider.
Conjecture.Money	ISO 4217 currency codes, scaled decimal amounts, rounding modes.
Conjecture.Regex	Regex-driven strings, common formats (URL/UUID/email/IP), ReDoS hunter.
Conjecture.JsonSchema	Strategies that conform to a JSON Schema.
Conjecture.Protobuf	Strategies shaped by a Protobuf MessageDescriptor.
Output & visualization
Conjecture.Formatters	JSON / NDJSON formatters for standalone data generation.
Conjecture.Interactive	Strategy preview, histograms, shrink traces (plain text).
Conjecture.LinqPad	LINQPad rich HTML formatters and shrink-trace visualizers.
Interactions
Conjecture.Interactions	Transport-agnostic abstractions: IInteraction, InteractionStateMachine<TState>.
Conjecture.Http	HttpInteraction and IHttpTarget.
Conjecture.Grpc	GrpcInteraction and IGrpcTarget covering all four RPC modes.
Conjecture.Messaging	Transport-agnostic message bus interactions + in-memory bus.
Conjecture.Messaging.AzureServiceBus	Azure Service Bus adapter.
Conjecture.Messaging.RabbitMq	RabbitMQ adapter.
Web & data
Conjecture.AspNetCore	Metadata-driven request synthesis for ASP.NET Core minimal APIs and MVC.
Conjecture.EFCore	Entity-graph strategies, roundtrip + migration invariants, IDbTarget.
Conjecture.AspNetCore.EFCore	Bridge for ASP.NET Core + EF Core integration tests.
Conjecture.OpenApi	Strategies derived from an OpenAPI 3 document.
Distributed
Conjecture.Aspire	Stateful property tests against .NET Aspire DistributedApplication.
Conjecture.Aspire.EFCore	Aspire + EF Core bridge with composite invariants.
Tooling
Conjecture.Mcp	Model Context Protocol server exposing Conjecture to AI assistants.
Conjecture.Tool	dotnet conjecture CLI for standalone data generation (in repo).
F#
Conjecture.FSharp	Idiomatic F# Gen<'a> wrappers and a PropertyRunner.
Conjecture.FSharp.Expecto	Expecto integration for Conjecture.FSharp.

Documentation

Full documentation is at ommundsen.dev/Conjecture:

• Quick Start — write your first property test in 5 minutes
• Tutorials — learn property-based testing step by step
• API Reference — auto-generated from source
• Porting Guide — coming from Python Hypothesis?
• Changelog

Credit

Conjecture is a .NET implementation of Hypothesis's property-based testing engine. The shrinking algorithm, choice-sequence IR, targeting, and example database all derive from the work of David R. MacIver, Zac Hatfield-Dodds, and the broader Hypothesis contributors. The C# API surface, source generators, and analyzer integrations are original to this project.

License

Source code: MPL-2.0 | NuGet packages: MIT