The purpose of testing is to increase confidence for stakeholders through evidence This is a good, succinct description of why you should write tests. Though,

The purpose of testing is to increase confidence for stakeholders through evidence This is a good, succinct description of why you should write tests. Though, as a solo developer who's considered sinking some time into writing tests for Report Card Writer, I've chosen not to. No amount of testing will help me make sales, which is my primary problem at the moment.