NUnit2057

Remove unnecessary lambda expression

Topic	Value
Id	NUnit2057
Severity	Info
Enabled	True
Category	Assertion
Code	DelegateUnnecessaryAnalyzer

Description

Only the argument value is needed by the Assert.

Motivation

The Assert method will call a delegate if passed in, but that is an unnecessary overhead.

In most cases, only the return value is needed by the assertion.

There are two exceptions:

1. When catching exceptions, like in:

   Assert.That(() => instance.Method1(null), Throws.ArgumentNullException);
   

2. When a method might need to be called multiple times, like in:

   Assert.That(() => task.IsCompleted, Is.True.After(5).Seconds.PollEvery(100).MilliSeconds);
   

Sometimes developers unnecessarily create a lambda expression for the actual parameter.

Assert.That(() => instance.Method1(Parameters), Is.EqualTo(expected));

Here, the call is performed inside the Assert and then the result is tested. This is not necessary. The same test can be written as:

Assert.That(instance.Method1(Parameters), Is.EqualTo(expected));

It is clearer both in looks and in what is being tested here.

Sometimes the lambda is created implicitly like in:

Assert.That(instance.Method2, Is.EqualTo(expected));

The fixed code should look like:

Assert.That(instance.Method2(), Is.EqualTo(expected));

This clearly indicates that the Assert is on the return value of the method.

How to fix violations

Remove the anonymous lambda creation () =>. There is a code-fix that can do this for you.

Configure severity

Via ruleset file

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

Via .editorconfig file

# NUnit2057: Remove unnecessary lambda expression
dotnet_diagnostic.NUnit2057.severity = chosenSeverity

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

Via #pragma directive

#pragma warning disable NUnit2057 // Remove unnecessary lambda expression
Code violating the rule here
#pragma warning restore NUnit2057 // Remove unnecessary lambda expression

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

#pragma warning disable NUnit2057 // Remove unnecessary lambda expression

Via attribute [SuppressMessage]

[System.Diagnostics.CodeAnalysis.SuppressMessage("Assertion",
    "NUnit2057:Remove unnecessary lambda expression",
    Justification = "Reason...")]