NUnit2012

Use StartsWithConstraint for better assertion messages in case of failure

Topic	Value
Id	NUnit2012
Severity	Info
Enabled	True
Category	Assertion
Code	StringConstraintUsageAnalyzer

Description

Using constraints instead of boolean methods will lead to better assertion messages in case of failure.

Motivation

Using Does.StartWith (or Does.Not.StartWith) constraint will lead to better assertion messages in case of failure, so this analyzer marks all usages of string StartsWith method where it is possible to replace with Does.StartWith constraint.

[Test]
public void Test()
{
    string actual = "...";
    string expected = "...";
    ClassicAssert.True(actual.StartsWith(expected));
}

How to fix violations

The analyzer comes with a code fix that will replace ClassicAssert.True(actual.StartWith(expected)) with Assert.That(actual, Does.StartWith(expected)). So the code block above will be changed into

[Test]
public void Test()
{
    string actual = "...";
    string expected = "...";
    Assert.That(actual, Does.StartWith(expected));
}

Configure severity

Via ruleset file

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

Via .editorconfig file

# NUnit2012: Use StartsWithConstraint for better assertion messages in case of failure
dotnet_diagnostic.NUnit2012.severity = chosenSeverity

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

Via #pragma directive

#pragma warning disable NUnit2012 // Use StartsWithConstraint for better assertion messages in case of failure
Code violating the rule here
#pragma warning restore NUnit2012 // Use StartsWithConstraint for better assertion messages in case of failure

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

#pragma warning disable NUnit2012 // Use StartsWithConstraint for better assertion messages in case of failure

Via attribute [SuppressMessage]

[System.Diagnostics.CodeAnalysis.SuppressMessage("Assertion",
    "NUnit2012:Use StartsWithConstraint for better assertion messages in case of failure",
    Justification = "Reason...")]