public void WhenTheHandlerExecutes(IEventFactory eventFactory, AddPremiumCommand addPremiumCommand) { var expectedEvent = Substitute.For <IEvent>(); var target = new AddPremiumCommandHandler(eventFactory); var contextId = Guid.NewGuid(); eventFactory.Create(contextId, Arg.Is <AddPremiumData>(data => data.PremiumId == addPremiumCommand.PremiumId && ExceptionHelpers.ExecuteSuccessfully(() => ValidateAddPremium(addPremiumCommand, data)))).Returns(expectedEvent); var result = target.Execute(contextId, addPremiumCommand); Assert.Contains(expectedEvent, result); }