public void GetOfferIdByRealEstateIdShouldThrowExceptionUponInvalidParameterPassed() { var realEstateId = ""; var serviceInstance = new OfferServices(context, imageServices.Object, cloudinaryServices.Object, userServices.Object, referenceNumberGenerator.Object, mapper ); Assert.ThrowsAsync <ArgumentNullException>(async() => serviceInstance.GetOfferIdByRealEstateIdAsync(realEstateId), ArgumentNullExceptonMessage); }