This is the same issue you have when you're building your own analytic system using SQL and you're building big queries to do more complex descriptive, and infe

This is the same issue you have when you're building your own analytic system using SQL and you're building big queries to do more complex descriptive, and inferential statistical shenanigans. No matter the technology, automated tests on known data with expected results are the only way to be sure what you're getting is right. And you better be sure, because people have zero tolerance for inaccurate analytics. They will immediately ignore your tool, permanently. For instance... if your slot machine analytic system does not include slot machines with apostrophe's in the name in its 'revenue total' column... you are so screwed. Even once you fix the bug, your stuff is tainted. Don't ask me how I know ;)