PosInformatique.Moq.Analyzers

PosInfoMoq1010: Use += null syntax when raising events with Raise()/RaiseAsync()

Property	Value
Rule ID	PosInfoMoq1010
Title	Use += null syntax when raising events with Raise()/RaiseAsync()
Category	Design
Default severity	Warning

Cause

When using Mock<T>.Raise() or Mock<T>.RaiseAsync(), the lambda expression used to identify the event should consistently use the += null syntax.

Rule description

While Moq is flexible and can identify the event even with += SomeMethod, using += null is the conventional and clearest way to indicate that you are merely referencing the event for Moq’s internal use, not actually subscribing a handler. This improves code readability and intent.

Example

public class Service
{
    public event EventHandler Changed;

    public void DoSomething()
    {
        this.Changed?.Invoke(this, EventArgs.Empty);
    }
}

Correct usage (+= null)

var serviceMock = new Mock<Service>();

// Clear intent: referencing the event for Moq
serviceMock.Raise(s => s.Changed += null, EventArgs.Empty);

Incorrect usage (+= SomeMethod)

public class MyTests
{
    private void MyEventHandler(object sender, EventArgs e) { /* ... */ }

    [Fact]
    public void Test()
    {
        var serviceMock = new Mock<Service>();

        // While functional, less clear intent
        serviceMock.Raise(s => s.Changed += MyEventHandler, EventArgs.Empty); // ⚠️
    }
}

How to fix violations

Change the lambda expression to use += null when identifying the event for Raise() or RaiseAsync().

Correct:

serviceMock.Raise(s => s.Changed += null, EventArgs.Empty);

Incorrect:

serviceMock.Raise(s => s.Changed += MyEventHandler, EventArgs.Empty);

When to suppress warnings

This is a design guideline for code readability. While suppressing it won’t cause runtime errors, it’s generally recommended to follow for consistent and clear code.

This site is open source. Improve this page.