What I keep running across, in different companies, different domains, different engineering styles is code that was written first with the intent to add code later... that ends up being untestable. It seems to be a common “design pattern” (in Java, at least) to add a Singleton that connects to a data store and reference that Singleton everywhere in the codebase - which means that using any of the code triggers a static method that tries to connect to remote Mongo/Cassandra/Postgres/Redis/something.
