NUnit2046

Use CollectionConstraint for better assertion messages in case of failure

Topic	Value
Id	NUnit2046
Severity	Info
Enabled	True
Category	Assertion
Code	UseCollectionConstraintAnalyzer

Description

Use Has.Length/Has.Count/Is.Empty instead of testing property directly.

Motivation

Consider the difference in error message between the following pairs of Asserts:

int[] array = { 1, 2 };
Assert.That(array.Length, Is.EqualTo(1));
Assert.That(array, Has.Length.EqualTo(1));

The first gives: Expected: 1, But was: 2, the second: Expected: property Length equal to 1, But was: 2 making it clear we talking about number of elements, not just a number.

The next example:

int[] array = { 1, 2 };
Assert.That(array.Length, Is.EqualTo(0));
Assert.That(array, Is.Empty);

This results in Expected: 0, But was: 2 in the first case and Expected: <empty>, But was: < 1, 2 > in the second.

int[] array = Array.Empty<int>();
Assert.That(array.Length, Is.GreaterThanOrEqualTo(1));
Assert.That(array, Is.Not.Empty);

This would change: Expected: greater than or equal to 1, But was: 0 into Expected: not <empty>, But was: <empty>

How to fix violations

Replace test on explicit .Length or .Count properties with Has.Length and Has.Count respectively. If testing against the value 0 use Is.Empty or Is.Not.Empty instead.

Configure severity

Via ruleset file

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

Via .editorconfig file

# NUnit2046: Use CollectionConstraint for better assertion messages in case of failure
dotnet_diagnostic.NUnit2046.severity = chosenSeverity

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

Via #pragma directive

#pragma warning disable NUnit2046 // Use CollectionConstraint for better assertion messages in case of failure
Code violating the rule here
#pragma warning restore NUnit2046 // Use CollectionConstraint for better assertion messages in case of failure

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

#pragma warning disable NUnit2046 // Use CollectionConstraint for better assertion messages in case of failure

Via attribute [SuppressMessage]

[System.Diagnostics.CodeAnalysis.SuppressMessage("Assertion",
    "NUnit2046:Use CollectionConstraint for better assertion messages in case of failure",
    Justification = "Reason...")]