Shouldly is an assertion framework which focuses on giving great error messages when the assertion fails while being simple and terse.

This is the old Assert way:

Assert.That(contestant.Points, Is.EqualTo(1337));

For your troubles, you get this message, when it fails:

Expected 1337 but was 0

How it Should be:

contestant.Points.ShouldBe(1337);

Which is just syntax, so far, but check out the message when it fails:

contestant.Points should be 1337 but was 0

It might be easy to underestimate how useful this is. Another example, side by side:

Assert.That(map.IndexOfValue("boo"), Is.EqualTo(2));    // -> Expected 2 but was -1
map.IndexOfValue("boo").ShouldBe(2);                    // -> map.IndexOfValue("boo") should be 2 but was -1

Shouldly uses the code before the ShouldBe statement to report on errors, which makes diagnosing easier.

Read more about Shouldly and its features at https://docs.shouldly.org/.

Shouldly can be found here on NuGet and can be installed by copying and pasting the following command into your Package Manager Console within Visual Studio (Tools > NuGet Package Manager > Package Manager Console).

Install-Package Shouldly

Alternatively if you're using .NET Core then you can install Shouldly via the command line interface with the following command:

dotnet add package Shouldly

To have ShouldMatchApproval display a diff of the expected and actual files, you will need to install the Shouldly.DiffEngine package and configure it.

Install-Package Shouldly.DiffEngine

ShouldMatchConfiguration.ShouldMatchApprovedDefaults.ConfigureDiffEngine();

Contributions to Shouldly are very welcome. For guidance, please see CONTRIBUTING.md