NUnit2055

Consider using Is.InstanceOf<T> constraint instead of an 'is T' expression

Description

Consider using Is.InstanceOf<T> instead of 'is T' expression for better assertion messages.

Motivation

Using the Is.InstanceOf<T> (or Is.Not.InstanceOf<T>) constraint will lead to better assertion messages when a test fails. This analyzer identifies usages of the is operator that can be replaced with Is.InstanceOf<T> to improve the quality of assertion messages.

[Test]
public void Test()
{
    Assert.That(instance1 is SomeType);
    Assert.That(instance2 is AnotherType, Is.True);
    Assert.That(instance3 is ThirdType, Is.False);
}

How to fix violations

The analyzer comes with a code fix that will replace Assert.That(instance is SomeType, Is.True) and Assert.That(instance is SomeType) into Assert.That(instance, Is.InstanceOf<SomeType>()) and similarly replace Assert.That(instance is SomeType, Is.False) into Assert.That(instance, Is.Not.InstanceOf<SomeType>()). So the code block above will be changed into

[Test]
public void Test()
{
    Assert.That(instance1, Is.InstanceOf<SomeType>());
    Assert.That(instance2, Is.InstanceOf<AnotherType>());
    Assert.That(instance3, Is.Not.InstanceOf<ThirdType>());
}

Configure severity

Via ruleset file

Configure the severity per project, for more info see MSDN.

Via .editorconfig file

# NUnit2055: Consider using Is.InstanceOf<T> constraint instead of an 'is T' expression
dotnet_diagnostic.NUnit2055.severity = chosenSeverity

where chosenSeverity can be one of none, silent, suggestion, warning, or error.

Via #pragma directive

#pragma warning disable NUnit2055 // Consider using Is.InstanceOf<T> constraint instead of an 'is T' expression
Code violating the rule here
#pragma warning restore NUnit2055 // Consider using Is.InstanceOf<T> constraint instead of an 'is T' expression

Or put this at the top of the file to disable all instances.

#pragma warning disable NUnit2055 // Consider using Is.InstanceOf<T> constraint instead of an 'is T' expression

Via attribute [SuppressMessage]

[System.Diagnostics.CodeAnalysis.SuppressMessage("Assertion",
    "NUnit2055:Consider using Is.InstanceOf<T> constraint instead of an 'is T' expression",
    Justification = "Reason...")]