Writing
Creating Instances, Using Inheritance: No Thank You!
Create instances for state or polymorphism and use inheritance for a common consumer. Static behavior and composition can keep testing from dictating every class's shape.
Topic
Static Classes
Classes whose members are used without constructing instances. Their language constraints, shared state and responsibilities determine when they suit a design.
2 pages
Writing
So You Think You Know C#? Static Classes
Choose static classes when instances serve no purpose. Shared type state, autonomous methods and immutable inputs explain the discipline that makes them useful.