You have been working as a tester in an Agile team You have found that...

You have been working as a tester in an Agile team You have found that the user stories are being defined by the team but it is still unclear what will be a successful outcome Even after story elaboration you are still unclear as to what a story should do As a result, you're not really sure what to test or to know when you'll be done with testing This problem is becoming worse as completed stories are showcased but the product owner is unhappy with the results

You've looked into the matter further and the comments from the product owner indicate that features are missing from the stories. The story is functioning correctly within the limited definition of the story but the product owner is expecting more functionality, such as error handling that isn't being defined in the story

What technique should you implement that would help to further define the product owner's expectations and alleviate the issues that are arising during the show cases?