MEPX
Chapter 9 of 10All chapters
  1. 1Objects and classes
  2. 2Encapsulation
  3. 3Inheritance
  4. 4Polymorphism
  5. 5Composition over inheritance
  6. 6Design principles
  7. 7Design patterns
  8. 8State and mutation
  9. 9Testing object code
  10. 10When not to use it

Chapter 9 of 10

Testing object code

What makes a class easy to test.

Seams

A class that creates its own database connection cannot be tested without one. The same class receiving that connection can be handed a fake, which is why injection matters.

  • Test through the public interface, not the private internals.
  • If a test needs to reach inside, the design is telling you something.

Fakes and mocks

A fake is a simple working substitute; a mock records how it was called. Mocking everything ties tests to implementation, so they break on refactors that changed nothing real.