Agent skill
fluent-assertions
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.
Install this agent skill to your Project
npx add-skill https://github.com/majiayu000/claude-skill-registry/tree/main/skills/other/other/fluent-assertions
SKILL.md
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
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