In looking over our codebase recently, I discovered that our tests on SceptrePlan are downright bad. Test coverage is poor, it doesn't really test all the functionality, and they're not very easy to read or maintain.
Ideally, we would have tests that cover all "public" methods of the class and validate the expected outcomes against the actual outcomes.
This is a very useful, low-risk opportunity for those looking to contribute to Sceptre.