XUnit - Testing event handlers

Testing event handlers in XUnit can be done through the Assert.Raises method. This method expect 3 parameters:

• An action of EventHandler<T> to attach a handler
• An action of EventHandler<T> to detach the handler
• An action containing the code that should trigger the event

This was not immediately clear to me so here is a (simple) example:

	[Fact]
	public void NotCompletingAUnitOfWork_Triggers_FailedEvent()
	{
	//Arrange
	var unitOfWorkFactory = _container.Resolve<IUnitOfWorkFactory>();
	var queryFactory = _container.Resolve<IQueryFactory>();
	//Act
	var uow = unitOfWorkFactory.Create();
	var customers = queryFactory
	.Query("GetCustomers")
	.List<Customer>();
	//Assert
	Assert.Raises<UnitOfWorkFailedEventArgs>(handler => uow.Failed += handler, handler => uow.Failed -= handler, () => uow.Dispose());
	}

view raw TestingEventHandlers.cs hosted with ❤ by GitHub

And here is the interface of the IUnitOfWork that is tested above:

	public interface IUnitOfWork: IDisposable
	{
	/// <summary>
	/// This event is raised when this UOW is successfully completed.
	/// </summary>
	event EventHandler<UnitOfWorkCompletedEventArgs> Completed;
	/// <summary>
	/// This event is raised when this UOW is failed.
	/// </summary>
	event EventHandler<UnitOfWorkFailedEventArgs> Failed;
	/// <summary>
	/// Completes this unit of work.
	/// It saves all changes and commit transaction if exists.
	/// </summary>
	void Complete();
	/// <summary>
	/// Completes this unit of work.
	/// It saves all changes and commit transaction if exists.
	/// </summary>
	Task CompleteAsync();
	}

view raw IUnitOfWork.cs hosted with ❤ by GitHub