Coverage is: - a negative signal (“low” coverage = no coverage) - not a positive signal (“high” coverage only means code paths were reached) - doesn’t mean y

Coverage is: - a negative signal (“low” coverage = no coverage) - not a positive signal (“high” coverage only means code paths were reached) - doesn’t mean your tests are thorough - doesn’t mean your tests are correct - most importantly for my current work, doesn’t mean you even have an accurate number (istanbul reports 100% coverage if it doesn’t instrument anything; nested languages aren’t instrumented at all, good luck finding out coverage of an XSL transform in JS) - (still relevant to my work) a good way of conveying safety of small, methodical refactors that can be eyeballed along with incremental changes to see they’re logically equivalent