The programming/math test introduces a "made up" programming language, and tests you on how it would work. Not terribly difficult, but definitely different then most technical interview questions (there were also some standard "write pseudocode/code to solve x" questions as well)
Sigiloso
Through questions like this, interviewers are mostly trying to test your skillset (and its relevance to the role) as robustly as possible, so be prepared for multiple offshoots and followups. It could be a useful exercise to do mocks with friends or colleagues in Epic to get a real sense of what the interview is actually like. Alternatively Prepfully has a ton of Epic Software Developer Intern experts who provide mock interviews for a pretty reasonable amount. prepfully.com/practice-interviews