Why is it important to define an interface for local data sources in application architecture?

Defining an interface for local data sources in an application architecture is important for several reasons:

• Abstraction and encapsulation: the interface hides implementation details, allowing changes in data storage methods without affecting the rest of the application.
• Testability: interfaces make it easier to create mocks or stubs for unit testing, improving code quality.
• Flexibility and extensibility: new data source implementations (e.g., database, cache, files) can be added without changing client code.
• Support for SOLID principles: especially the interface segregation and dependency inversion principles.

For example, a LocalDataSource interface might include methods for reading and writing data, with implementations using Room, SharedPreferences, or file system.