These charts are useful to pinpoint bugs related to scaling. Usually the desired outcome for the pie chart is to be a solid color, indicating 100% success. However, the definition of “success” is actually configurable; you may want to write negative tests, which means that in a properly working system, the scenario must fail. For example, you may want to test the API rate limit. In these cases, a successful outcome will include a graphic that accurately displays less than 100% success.