Dependency Breaking Technique Executor

Example 1: Parameterize Constructor (Java)

PaymentProcessor creates new DatabaseConnection("prod", 5432) in its constructor. Tests cannot run without a live database.

Technique: Parameterize Constructor. Add PaymentProcessor(DatabaseConnection db) constructor; original becomes this(new DatabaseConnection(...)). Tests inject new FakeDatabaseConnection(). Production callers unchanged.

Example 2: Extract Interface (Java)

UserNotifier holds a UserRepository field. Repository opens a database on construction; no way to substitute.

Technique: Extract Interface. Create empty IUserRepository; make UserRepository implements IUserRepository; change UserNotifier's field type. Compile — errors identify every method that must appear on the interface. Create FakeUserRepository for tests. Production unchanged.

Example 3: Push Down Dependency (C++)

OffMarketTradeValidator.showMessage() calls AfxMessageBox (Windows MFC) and g_dispatcher. Cannot test validation logic without the Windows GUI framework.

Technique: Push Down Dependency. Make showMessage() pure virtual in the base class. WindowsOffMarketTradeValidator holds real MFC code. TestingOffMarketTradeValidator overrides showMessage() with an empty body. Tests instantiate the testing subclass — validation logic is now testable without any UI framework. (See case study cs-012 in references/all-techniques.md.)