fluent-assertions

name	fluent-assertions
description	Writes fluent, readable test assertions and validations using FluentAssertions library. Use when: Writing unit tests, validating service responses, asserting domain entity states, testing collections and async operations.
allowed-tools	Read, Edit, Write, Glob, Grep, Bash

FluentAssertions Skill

FluentAssertions provides a fluent API for expressing test assertions in C#. In VanDaemon, it's used alongside xUnit and Moq for testing services, controllers, plugins, and the JsonFileStore persistence layer. The library produces clear failure messages that explain exactly what went wrong.

Quick Start

Basic Value Assertions

// From VanDaemon test patterns
result.Should().NotBeNull();
result.Should().Be(expectedValue);
tank.CurrentLevel.Should().BeInRange(0, 100);
tank.IsActive.Should().BeTrue();

Collection Assertions

// Testing tank service returns
var tanks = await tankService.GetAllTanksAsync();
tanks.Should().NotBeNull();
tanks.Should().HaveCount(3);
tanks.Should().AllSatisfy(t => t.IsActive.Should().BeTrue());
tanks.Should().Contain(t => t.Type == TankType.FreshWater);

Async Operation Assertions

// Testing async service methods
await service.Invoking(s => s.GetTankByIdAsync(Guid.Empty))
    .Should().ThrowAsync<ArgumentException>();

var result = await service.GetAllControlsAsync();
result.Should().BeEquivalentTo(expectedControls);

Key Concepts

Concept	Usage	Example
Should()	Entry point for all assertions	value.Should().Be(5)
BeEquivalentTo()	Deep object comparison	actual.Should().BeEquivalentTo(expected)
AllSatisfy()	Assert condition on all items	list.Should().AllSatisfy(x => x.IsActive.Should().BeTrue())
Invoking()	Test exception throwing	obj.Invoking(x => x.Method()).Should().Throw<T>()
Because()	Custom failure message	value.Should().Be(5, "configuration requires this")

Common Patterns

Service Response Validation

When: Testing application services like TankService, ControlService

var mockFileStore = new Mock<IJsonFileStore>();
mockFileStore.Setup(x => x.LoadAsync<List<Tank>>("tanks.json", It.IsAny<CancellationToken>()))
    .ReturnsAsync(testTanks);

var service = new TankService(logger, mockFileStore.Object);
var result = await service.GetAllTanksAsync();

result.Should().NotBeNull();
result.Should().HaveCount(2);
result.First().Name.Should().Be("Fresh Water");

Entity State Assertions

When: Validating domain entity properties

var tank = new Tank { Type = TankType.FreshWater, AlertLevel = 10 };
tank.Type.Should().Be(TankType.FreshWater);
tank.AlertLevel.Should().BeGreaterThanOrEqualTo(0);
tank.AlertWhenOver.Should().BeFalse("fresh water alerts when level drops below threshold");

See Also

• patterns - Assertion patterns by type
• workflows - Testing workflows and best practices

Related Skills

• xunit skill for test framework fundamentals
• moq skill for mocking dependencies before asserting results
• csharp skill for language features used in assertions