Event Impersonation

Creating an imposter

Define the target interface and enable generation:

Example

using System;
using System.Threading.Tasks;
using Imposter.Abstractions;
using Imposter.Tests.Features.EventImpersonation;

[assembly: GenerateImposter(typeof(IEventSetupSut))]

public interface IEventSetupSut
{
    event EventHandler SomethingHappened;

    event Func<object?, EventArgs, Task>? AsyncSomethingHappened;

    event Func<object?, EventArgs, ValueTask>? ValueTaskSomethingHappened;

    event AsyncEventHandler<EventArgs>? CustomAsyncSomethingHappened;
}

public delegate Task AsyncEventHandler<in TEventArgs>(object? sender, TEventArgs args)
    where TEventArgs : EventArgs;

Subscribe/Unsubscribe Verification

Example

EventHandler h = (s, e) => { };

service.SomethingHappened += h;
service.SomethingHappened -= h;

imposter.SomethingHappened.Subscribed(h, Count.Once());
imposter.SomethingHappened.Unsubscribed(h, Count.Once());

Raise an event

Example

// Raise in-order for current subscribers
imposter.SomethingHappened.Raise(this, EventArgs.Empty);

Note

• Raise(sender, args) notifies the handlers currently subscribed at the time of the call, in subscription order.
• If no one is subscribed, Raise is a no-op.
• Exceptions thrown by a handler bubble up and stop further handlers unless your SUT or test catches them (see Event Exceptions).

Interceptors and Invocation Counts

Example

// Observe subscriptions/unsubscriptions
imposter.SomethingHappened.OnSubscribe(handler => { /* inspect */ });
imposter.SomethingHappened.OnUnsubscribe(handler => { /* inspect */ });

// Verify handler invocation count
imposter.SomethingHappened.HandlerInvoked(Arg<EventHandler>.Is(h), Count.Exactly(2));