Raising events

FakeItEasy can be used to simulate the raising of an event from a Fake object, assuming the event is virtual or abstract, or defined on an interface.

EventHandler-based events

Suppose a standard EventHandler-based event such as this one:

public interface IRobot
    event EventHandler FellInLove;

You can raise that event, specifying sender and event arguments. You could also omit the sender and the Fake will be passed as sender to the event handler, and there's also a convenience method for raising with empty event arguments:

var robot = A.Fake<IRobot>();

// Somehow use the fake from the code being tested

// Raise the event!
robot.FellInLove += Raise.With(someEventArgs); // the "sender" will be robot

// Use the overload for empty event args. Sender will be robot, args will be EventArgs.Empty
robot.FellInLove += Raise.WithEmpty();

// Specify sender and event args explicitly:
robot.FellInLove += Raise.With(sender: robot, e: someEventArgs);

VB.NET syntax

' Raise the event!
AddHandler robot.FellInLove, Raise.With(someEventArgs) ' the "sender" will be robot

' Use the overload for empty event args. Sender will be robot, args will be EventArgs.Empty
AddHandler robot.FellInLove, Raise.WithEmpty()

' Specify sender and event args explicitly:
AddHandler robot.FellInLove, Raise.With(sender, someEventArgs)

Raising EventHandler<TEventArgs>

Events of type EventHandler<TEventArgs> can be raised in exactly the same way.

Note that for the .NET 4.0 version of the FakeItEasy library, TEventArgs needs to extend EventArgs to support the above syntax. Otherwise, the event must be raised as if it were a "free-form" event as described below.

"Free-form" events using arbitrary delegates

It is also possible to raise events defined using a custom delegate (a.k.a "free-form delegate"), like these:

public delegate void FreeformEventHandler(int count);
public delegate void CustomEventHandler(object sender, CustomEventArgs e); // considered a custom
                                                                           // delegate in .NET 4.0
event FreeformEventHandler FreeformEvent;
event CustomEventHandler CustomEvent;

From C#

To raise a free-form event from C#, use Raise.FreeForm.With, which automatically infers the correct delegate type:

fake.FreeformEvent += Raise.FreeForm.With(7);
fake.CustomEvent += Raise.FreeForm.With(fake, sampleCustomEventArgs);

Due to language limitations, Raise.Freeform.With does not work in VB.NET, and it uses late binding, so you need a reference to the Microsoft.CSharp assembly in order to use it.


To raise a free-form event from VB.NET, you must use Raise.FreeForm(Of TEventHandler).With:

AddHandler fake.FreeformEvent, Raise.FreeForm(Of FreeformEventHandler).With(7)
AddHandler fake.CustomEvent, Raise.FreeForm(Of CustomEventHandler).With(fake, sampleCustomEventArgs)

Specifying the type of the event handler gets around the language restrictions in VB.NET. This method may also be used from C# if you don't want to rely on late binding.