In software development, singletons are widely discouraged and frowned upon — but with good reason. They are difficult or impossible to test, and they entangle your codebase when used implicitly in other classes, making code reuse difficult. Most of the time, a singleton amounts to nothing more than a disguise for global, mutable state. Everyone knows at least knows that is a terrible idea. However, singletons are occasionally an unavoidable and necessary evil. How can we incorporate them into our code in a clean, modular, and testable way?