NUnit3001

Expression was checked in an ClassicAssert.NotNull, ClassicAssert.IsNotNull or Assert.That call

Description

This rule check diagnostics reported by the CS8601-CS8607 and CS8629 compiler errors:

CS8602: Dereference of a possibly null reference.

It then checks the previous statements for one of:

• ClassicAssert.NotNull(...)
• ClassicAssert.IsNotNull(...)
• Assert.That(..., Is.Not.Null)

For the same expression as the one that raised the original compiler error. If found, the compiler error is suppressed.

The rule also covers CS8629: Nullable value type may be null

In this case, the previous statement is allowed to be one of:

• Assert.That(...HasValue)
• Assert.That(...HasValue, Is.True)
• ClassicAssert.True(...HasValue)
• ClassicAssert.IsTrue(...HasValue)

The exception is that if the statement is part of an Assert.Multiple it is not suppressed, as in this case the statement containing the compiler error will be executed.

Motivation

[TestFixture]
internal sealed class SomeClassFixture
{
    private SomeClass instance;

    [SetUp]
    public void Setup()
    {
        instance = new SomeClass();
    }

    [Test]
    public void Test()
    {
        string? result = instance.MethodUnderTest();
        Assert.That(result, Is.Not.Null);
        Assert.That(result.Length, Is.GreaterThan(0));
    }

    [Test]
    public void TestMultiple()
    {
        string? result = instance.MethodUnderTest();
        Assert.Multiple(() =>
        {
            Assert.That(result, Is.Not.Null);
            Assert.That(result.Length, Is.GreaterThan(0));
        });
    }
}

In the above fixture the compiler would give a warnings because result can be null and the compiler knows nothing about the Assert.That(result, Is.Not.Null); statement.

The first occurrence - in the Test method - will be suppressed, the second - in the TestMultiple - will not.

How to fix violations

Ensure that the reference is not null before dereferencing it. This can be done using regular C# language constructs or NUnit assertions.

Configure severity

The rule has no severity, but can be disabled.

Via ruleset file

To disable the rule for a project, you need to add a ruleset file

<?xml version="1.0" encoding="utf-8"?>
<RuleSet Name="NUnit.Analyzer Suppressions" Description="DiagnosticSuppression Rules" ToolsVersion="12.0">
  <Rules AnalyzerId="DiagnosticSuppressors" RuleNamespace="NUnit.NUnitAnalyzers">
    <Rule Id="NUnit3001" Action="Info" /> <!-- Possible Null Reference -->
    <Rule Id="NUnit3002" Action="Info" /> <!-- NonNullableField/Property is Uninitialized -->
    <Rule Id="NUnit3003" Action="Info" /> <!-- Avoid Uninstantiated Internal Classes -->
    <Rule Id="NUnit3004" Action="Info" /> <!-- Types that own disposable fields should be disposable -->
  </Rules>
</RuleSet>

and add it to the project like:

<PropertyGroup>
  <CodeAnalysisRuleSet>NUnit.Analyzers.Suppressions.ruleset</CodeAnalysisRuleSet>
</PropertyGroup>

For more info about rulesets see MSDN.

Via .editorconfig file

This is currently not working. Waiting for Roslyn

# NUnit3001: Expression was checked in an ClassicAssert.NotNull, ClassicAssert.IsNotNull or Assert.That call
dotnet_diagnostic.NUnit3001.severity = none