Google Testing Blog: Simplify Your Code: Functional Core, Imperative Shell

Learn how to separate business logic from side effects using the functional core, imperative shell pattern. The approach isolates pure, testable business logic in a functional core while handling I/O operations, database calls, and external interactions in an imperative shell. This separation makes code more testable, maintainable, and reusable by allowing core logic to be tested in isolation and shells to be easily modified or swapped.