PosInformatique.Moq.Analyzers

PosInfoMoq2018: The first parameter of Raise()/RaiseAsync() must be an event

Property	Value
Rule ID	PosInfoMoq2018
Title	The first parameter of Raise()/RaiseAsync() must be an event
Category	Compilation
Default severity	Error

Cause

The first parameter passed to Raise() or RaiseAsync() must reference an event member of the mocked type.
Using any other kind of member (property, method, field, etc.) is invalid.

Rule description

When using Moq, Mock<T>.Raise() and Mock<T>.RaiseAsync() are designed to trigger events defined in the mocked type.
If the provided lambda expression instead references something that is not an event (like a property assignment), the code is invalid.

Example

public class Service
{
    public event EventHandler Changed;
    public event EventHandler<DataEventArgs> DataChanged;
    public int Property { get; set; }
}

public class DataEventArgs : EventArgs
{
    public int Value { get; }
    public DataEventArgs(int value) => Value = value;
}

Correct usage (event targeted)

var serviceMock = new Mock<Service>();

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

// Raise() with EventHandler<T>
serviceMock.Raise(s => s.DataChanged += null, new DataEventArgs(42));

// RaiseAsync() with EventHandler<T>
await serviceMock.RaiseAsync(s => s.DataChanged += null, new DataEventArgs(42));

Incorrect usage (invalid target)

var serviceMock = new Mock<Service>();

// Refers to a property, not an event
serviceMock.Raise(s => s.Property = 10, EventArgs.Empty);    // ❌

// Same problem with RaiseAsync
await serviceMock.RaiseAsync(s => s.Property = 10, EventArgs.Empty);    // ❌

How to fix violations

Ensure that the first parameter of Raise() and RaiseAsync() always references an event of the mocked type, never a property or field.

Correct:

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

Incorrect:

serviceMock.Raise(s => s.Property = 10, EventArgs.Empty);

When to suppress warnings

Do not suppress this warning. If bypassed, Moq itself will throw an ArgumentException exception at runtime with a message such as Unsupported expression: m => (m.Property = 10).

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