What best describes a stub in programming?

A stub in programming is best described as an incomplete function that is created with basic input and output to facilitate testing or development. Stubs allow developers to simulate the behavior of complex systems or components that have not yet been fully implemented. By using a stub, developers can test the integration of various parts of a system without needing the complete functionality of every component.

For example, if a developer is working on a system that relies on a database, but the database connection is not yet available, they might create a stub that mimics how the database would respond to certain queries. This way, they can continue testing related functions without interruption, ensuring progress on the overall project.

The other options describe different concepts in programming. A fully implemented function refers to a component that has full functionality and does not match the description of a stub. A method for data validation specifically pertains to checking input values, which is unrelated to the concept of stubs. Lastly, error handling encompasses techniques for managing errors in a program, which also does not align with the definition of a stub.