public async Task Commands_WhenExecuting_CanHandleValidationErrors()
{
// Arrange
var handlerFactory = new MessageHandlerRegistry();
var mediator = new Mediator(handlerFactory.MultiInstanceFactory, handlerFactory.SingleInstanceFactory);
handlerFactory.AddHandlersForCommandOrQuery<ICommandHandler<TestCommand>>(new TestCommandHandler(mediator));
// Act
var result = await mediator.Send(new TestCommand { Id = 999 });
// Assert
Assert.IsTrue(result.ValidationResults.Any());
}