Lesson 12: Testing, mocks, and seams

This lesson practices Testing, mocks, and seams at real C# application level. We start from design pain, study code, practice a small decision, predict behavior, and verify mastery.

Design seams so behavior can be tested without real infrastructure.

Testing, mocks, and seams: Design seams so behavior can be tested without real infrastructure.
design pressure: A repeated change, duplication, or test pain that signals the model needs a better boundary.