Fluent Assertions – Working with Exceptions

When writing automated tests, verifying that a certain piece of code throws the expected exception is just as important as verifying positive outcomes. Fluent Assertions in C# makes exception testing more readable, expressive, and less error-prone compared to traditional Assert.Throws syntax.

Why Test for Exceptions?

Exception testing ensures that your application behaves correctly in edge cases and error scenarios. For example:

  • When invalid input should trigger an exception
  • When certain operations are not allowed
  • When dependencies fail and your code must handle it gracefully

Traditional xUnit Exception Testing


[Fact]
public void Divide_By_Zero_Should_Throw_Exception()
{
    Assert.Throws<DivideByZeroException>(() => Calculator.Divide(10, 0));
}

This works fine, but it’s not as expressive and doesn’t allow detailed inspection of the exception message in a clean way.

Exception Testing with Fluent Assertions

Fluent Assertions makes this much easier and more expressive:


[Fact]
public void Divide_By_Zero_Should_Throw_Exception()
{
    Action act = () => Calculator.Divide(10, 0);

    act.Should()
       .Throw<DivideByZeroException>()
       .WithMessage("*divide by zero*");
}

Key Benefits:

  • Readable chain of assertions
  • Ability to verify exception type and message
  • Supports wildcards in messages (*text*)

Capturing the Exception for Further Assertions

Sometimes, you may need to inspect additional properties of the exception:


[Fact]
public void Invalid_Operation_Should_Contain_Extra_Details()
{
    Action act = () => OrderService.ProcessOrder(null);

    var exception = act.Should()
                       .Throw<InvalidOperationException>()
                       .Which;

    exception.Data["OrderId"].Should().BeNull();
}

Async Exception Testing

For asynchronous methods, Fluent Assertions provides an await act.Should().ThrowAsync<T>() syntax:


[Fact]
public async Task Async_Method_Should_Throw_Exception()
{
    Func<Task> act = async () => await UserService.CreateUserAsync(null);

    await act.Should()
             .ThrowAsync<ArgumentNullException>()
             .WithMessage("*username*");
}

Best Practices for Exception Testing

  • Test both exception type and message when applicable
  • Use wildcard matching for messages to avoid brittle tests
  • For async methods, always use ThrowAsync
  • Keep tests focused on one scenario per method

📣 I’d Love Your Feedback

Was this helpful? Have scenarios you want covered (e.g., dictionaries, sets, or deep-object comparisons)? Share your suggestions, and I’ll explore them next.

🔔 Stay connected and follow HGDevHub for more micro tools, automation scripts, and tech walkthroughs:

📩 Stay Tuned

More automation scripts and micro-tools coming soon. Follow HGDevHub for fresh tools that save time and spark ideas.

Comments

Post a Comment

Popular posts from this blog

Fluent Assertions in C# with xUnit – Clean and Readable Unit Tests

Category: Technology Tags: C#, xUnit, FluentAssertions, Unit Testing, .NET ✅ Introduction Unit tests are crucial for maintaining healthy and predictable codebases. Traditional assertions like Assert.Equal() in xUnit get the job done, but they can often be less readable , especially when your test logic grows. This is where Fluent Assertions comes in — it makes your unit test statements more expressive, human-readable , and developer-friendly . 💡 What Is Fluent Assertions? Fluent Assertions is a popular .NET library that allows you to write unit test assertions in a more natural, fluent syntax. This improves both readability and maintainability of your test code. 📦 NuGet Package: FluentAssertions 🌐 GitHub: https://github.com/fluentassertions/fluentassertions 🔧 Setting Up Fluent Assertions in xUnit Step 1: Install via NuGet dotnet add package FluentAssertions Or through the NuGet Package Manager in Visual Studio. ✍️ Example: Traditional vs Fluent Assertions Le...
Read more

Auto-Open URLs with Node.js – A Beginner-Friendly Script

Want to automate opening a specific URL in your browser multiple times? Whether you're testing link behavior, demoing an app, or running an automation sequence — this simple Node.js script does the job. 🛠️ What This Script Does Opens any given URL in Chrome or Edge Lets you choose how many times (tabs) you want it to open Works from the command line with just one command 📦 Prerequisites Node.js installed on your system Install the open package via terminal: npm install open 💡 The Node.js Script Create a file named index.js and paste the code below: // index.js const open = require("open").default; // 🌐 URL to open const url = "https://hiddengemsatlas.blogspot.com/2025/08/auto-open-urls-with-nodejs-beginner.html"; // Replace this with your URL // ✅ Map browser IDs to app names const browserMap = { 1: "chrome", 2: "msedge", }; // 🧾 Get command-line arguments const [, , browserIdArg, countArg] = pro...
Read more

Top 7 Must-Watch Anime for Beginners: Your Gateway to an Epic Adventure

Image
Anime isn't just a genre; it's an experience. Whether you've seen snippets on TV, heard about it from friends, or stumbled upon it while scrolling through social media, anime has undoubtedly piqued your curiosity. But where do you even begin? If you're new to the world of anime, don’t worry! We’ve got you covered. Here’s a list of 7 must-watch anime that will ease you into the captivating world of Japanese animation. Each one offers a unique experience that’ll keep you hooked from the first episode! 1. Naruto – The Classic Hero's Journey Genre: Action, Superhero, School Why watch? Strong character development Epic fight scenes Inspirational themes of never giving up Follow Naruto Uzumaki, a young ninja with big dreams of becoming the Hokage, the leader of his village. Full of heart-pounding action, powerful friendships, and heartfelt moments, Naruto's journey is one of perseveran...
Read more