Business users at cloud kicks have just completed user acceptance testing for a Commence cloud...

This answer states that number of passed test cases divided by total number of test cases is how the success rate is calculated after completing user acceptance testing (UAT) for a Commerce Cloud implementation at CK. Test cases are scenarios or steps that verify or validate if a feature or a functionality meets the acceptance criteria or requirements. Passed test cases are test cases that meet or pass the acceptance criteria or requirements. Total number of test cases are all test cases that are executed or performed for UAT. Number of passed test cases divided by total number of test cases is how the success rate is calculated because it measures how many test cases meet or pass the acceptance criteria or requirements out of all test cases executed or performed for UAT. References: https://trailhead.salesforce.com/en/content/learn/modules/salesforce-business-analyst-quick-look/use-user-stories-to-capture-requirements