Nullables: Testing Without Mocks

STARTER_CHARACTER = ⭕️

Nullables are production code with an off switch: classes with external I/O anywhere in their dependencies offer create() (real) and createNull() (I/O disabled, everything else runs normally). Tests are narrow (focused on one class), sociable (dependencies run for real), and state-based (assert outputs and state, never method calls). Don't use mocking libraries or DI frameworks — Nullables make them unnecessary.

The cut

Stub at the lowest point — the third-party edge — never your own code:

OrderService  →  PaymentClient  →  HttpClient  →  third-party lib
  app code       high-level        low-level       ✂ stubbed when nulled
                 wrapper           wrapper