Testable WinForms Applications (MVP pattern)

WinForms applications are largely legacy systems due to WPF's rising popularity, though they remain relevant for upgrading existing software or situations demanding high performance. Testing WinForms apps is often debated, with concerns about the tight coupling between UI events and business logic. However, separating the application into Data, User Interface, and Business Logic components using the Model-View-Presenter (MVP) pattern enhances testability. The MVP pattern involves creating interfaces to define interactions between the View (UI), Presenter (business logic), and Model (data). The example uses an `IProductView` interface for the View and a `ProductPresenter` to handle user interactions and data access. A `IProductDataAccess` interface abstracts data access operations. The presenter's dependencies are injected through the constructor, simplifying testing and promoting modularity. A test case demonstrates mocking external dependencies using a substitute to verify the `AddProduct` method's call. This approach promotes loose coupling and makes the application more maintainable and testable. Starting with high-level components and defining clear interfaces is crucial for creating robust and testable applications.