PosInfoMoq2017.md

PosInfoMoq2017: Mock<T>.Raise()/RaiseAsync() must use parameters matching the event signature

Property	Value
Rule ID	PosInfoMoq2017
Title	Mock<T>.Raise()/RaiseAsync() must use parameters matching the event signature
Category	Compilation
Default severity	Error

Cause

The parameters passed to Raise() or RaiseAsync() must exactly match the parameters of the corresponding event delegate.

Rule description

When mocking events with Moq, calling Mock<T>.Raise() or Mock<T>.RaiseAsync() requires that the provided arguments match the event signature.

• With the Raise(event, EventArgs) overload:

  • Used for EventHandler or EventHandler<T>.
  • Moq automatically supplies the sender (the mocked object).
  • You only pass the EventArgs (or derived class) instance.

• With the Raise(event, params object[]) overload:

  • You provide all the arguments of the event delegate yourself.
  • This includes the sender and all additional event arguments.

Example

public class Service
{
    public event EventHandler Changed;
    public event EventHandler<DataEventArgs> DataChanged;

    public void DoSomething()
    {
        this.Changed?.Invoke(this, EventArgs.Empty);
        this.DataChanged?.Invoke(this, new DataEventArgs(42));
    }
}

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

Correct usage (matching parameters)

var serviceMock = new Mock<Service>();

// Raise with EventHandler (sender is mocked object, EventArgs required)
serviceMock.Raise(s => s.Changed += null, EventArgs.Empty);

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

// Raise with params object[] (sender + event args explicitly)
serviceMock.Raise(s => s.DataChanged += null, "CustomSender", new DataEventArgs(42));

Incorrect usage (parameters not matching)

var serviceMock = new Mock<Service>();

// Missing EventArgs
serviceMock.Raise(s => s.Changed += null);   // ❌

// Wrong argument type
serviceMock.Raise(s => s.DataChanged += null, EventArgs.Empty);   // ❌

How to fix violations

To fix a violation, ensure that the arguments passed to Raise() or RaiseAsync() match exactly the event delegate signature:

• EventHandler: (object sender, EventArgs e)
• EventHandler<T>: (object sender, T e)

Depending on the overload:

• With Raise(event, EventArgs) → provide only EventArgs or T.
• With Raise(event, params object[]) → provide both sender and EventArgs (or T).

When to suppress warnings

Do not suppress errors from this rule. If skipped, Moq will throw a runtime exception such as TargetParameterCountException (with the following message "Parameter count mismatch") or an ArgumentException to explain that a value can not be converted to an other type.