Here is a list of properties of tests. Not all tests need to exhibit all properties. However, no property should be given up without receiving a property of greater value in return.
Finding a mentor won't save you. Here's why the common leadership advice of "find a mentor" falls flat – and what you should seek out instead, as a leader.
There's one really common performance mistake I see constantly in Ruby/Rails web applications. It relies on a little-known and poorly-understood feature known as the ActiveRecord QueryCache.