Fsharp Testing

This covers the full F# testing stack: xUnit for structure, FsUnit for F# friendly assertions, Unquote for quotation based failure messages that actually tell you what broke, and FsCheck for property based testing. You get working examples of async tests with task, parameterized theories, custom generators, and both function stub patterns (the F# way) and NSubstitute for .NET interfaces. The integration testing section shows WebApplicationFactory setup with in-memory databases. Use this when you're setting up a new F# project's test suite or when your existing tests feel clunky because you're fighting against C# patterns. The anti-patterns section alone is worth reading if you've been writing Thread.Sleep in your async tests.

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last updated: Jul 14, 2026

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Install

$ npx -y skills add affaan-m/everything-claude-code --skill fsharp-testing --agent claude-code

Installs into .claude/skills of the current project.

Files

F# Testing Patterns

Comprehensive testing patterns for F# applications using xUnit, FsUnit, Unquote, FsCheck, and modern .NET testing practices.

When to Activate

Writing new tests for F# code
Reviewing test quality and coverage
Setting up test infrastructure for F# projects
Debugging flaky or slow tests

Test Framework Stack

Tool	Purpose
xUnit	Test framework (standard .NET ecosystem choice)
FsUnit.xUnit	F#-friendly assertion syntax for xUnit
Unquote	Assertion library using F# quotations for clear failure messages
FsCheck.xUnit	Property-based testing integrated with xUnit
NSubstitute	Mocking .NET dependencies
Testcontainers	Real infrastructure in integration tests
WebApplicationFactory	ASP.NET Core integration tests

Unit Tests with xUnit + FsUnit

Basic Test Structure

module OrderServiceTests

open Xunit
open FsUnit.Xunit

[<Fact>]
let ``create sets status to Pending`` () =
    let order = Order.create "cust-1" [ validItem ]
    order.Status |> should equal Pending

SKILL.md on GitHub