My favorite trick is binding a hook in unit test modules that basically runs an "explain q" for every query "q", and asserts that it found an appropriate index

My favorite trick is binding a hook in unit test modules that basically runs an "explain q" for every query "q", and asserts that it found an appropriate index to use. Then as long as your unit tests exercise all queries your app needs, you know that your database indices are appropriate for your app's usages.