What is the best way to do QA of tracking implementation?

My experience tells me that I always need to do end-to-end testing, just relying on that whenever an event ends up in segment, it will also end up in the destination in the right way, won't do. But, with that said, each event defined in the source and checked in the destination, seems to be enough. One lesson learned, is that sometimes a destination 'tells' us they accept a value as integer or datetime, but actually needed it as string. It's those things that make segment sometimes a bit tricky to implement.